refactor: replace Bearer token auth with HttpOnly cookies

- Remove POST /api/v1/register endpoint entirely
- Session creation (POST /api/v1/session) now sets neoirc_auth HttpOnly
  cookie instead of returning token in JSON body
- Login (POST /api/v1/login) now sets neoirc_auth HttpOnly cookie
  instead of returning token in JSON body
- Add PASS IRC command for setting session password (enables multi-client
  login via POST /api/v1/login)
- All per-request auth reads from neoirc_auth cookie instead of
  Authorization: Bearer header
- Cookie properties: HttpOnly, SameSite=Strict, Secure when behind TLS
- Logout and QUIT clear the auth cookie
- Update CORS to AllowCredentials:true with origin reflection
- Remove Authorization from CORS AllowedHeaders
- Update CLI client to use cookie jar (net/http/cookiejar)
- Remove Token field from SessionResponse
- Add SetPassword to DB layer, remove RegisterUser
- Comprehensive test updates for cookie-based auth
- Add tests: TestPassCommand, TestPassCommandShortPassword,
  TestPassCommandEmpty, TestSessionCookie
- Update README extensively: auth model, API reference, curl examples,
  security model, design principles, roadmap

closes #83

Makefile

@@ -1,4 +1,4 @@
-.PHONY: all build lint fmt fmt-check test check clean run debug docker hooks
+.PHONY: all build lint fmt fmt-check test check clean run debug docker hooks ensure-web-dist
 
 BINARY := neoircd
 VERSION := $(shell git describe --tags --always --dirty 2>/dev/null || echo "dev")
@@ -7,10 +7,21 @@ LDFLAGS := -X main.Version=$(VERSION) -X main.Buildarch=$(BUILDARCH)
 
 all: check build
 
-build:
+# ensure-web-dist creates placeholder files so //go:embed dist/* in
+# web/embed.go resolves without a full Node.js build.  The real SPA is
+# built by the web-builder Docker stage; these placeholders let
+# "make test" and "make build" work outside Docker.
+ensure-web-dist:
+	@if [ ! -d web/dist ]; then \
+		mkdir -p web/dist && \
+		touch web/dist/index.html web/dist/style.css web/dist/app.js && \
+		echo "==> Created placeholder web/dist/ for go:embed"; \
+	fi
+
+build: ensure-web-dist
 	go build -ldflags "$(LDFLAGS)" -o bin/$(BINARY) ./cmd/neoircd
 
-lint:
+lint: ensure-web-dist
 	golangci-lint run --config .golangci.yml ./...
 
 fmt:
@@ -20,7 +31,7 @@ fmt:
 fmt-check:
 	@test -z "$$(gofmt -l .)" || (echo "Files not formatted:" && gofmt -l . && exit 1)
 
-test:
+test: ensure-web-dist
 	go test -timeout 30s -v -race -cover ./...
 
 # check runs all validation without making changes

README.md

@@ -115,7 +115,7 @@ Everything else is IRC. `PRIVMSG`, `JOIN`, `PART`, `NICK`, `TOPIC`, `MODE`,
 Joining a nonexistent channel creates it. Channels disappear when empty. Nicks
 are unique per server. Identity starts with a key — a nick is a display name.
 Accounts are optional: you can create an anonymous session instantly, or
-register with a password for multi-client access to a single session.
+set a password via the PASS command for multi-client access to a single session.
 
 ### On the resemblance to JSON-RPC
 
@@ -149,63 +149,59 @@ not arbitrary choices — each one follows from the project's core thesis that
 IRC's command model is correct and only the transport and session management
 need to change.
 
-### Identity & Sessions — Dual Authentication Model
+### Identity & Sessions — Cookie-Based Authentication
 
-The server supports two authentication paths: **anonymous sessions** for
-instant access, and **optional account registration** for multi-client access.
+The server uses **HTTP cookies** for all authentication. There is no separate
+registration step — sessions start anonymous and can optionally set a password
+for multi-client access.
 
-#### Anonymous Sessions (No Account Required)
-
-The simplest entry point. No registration, no passwords.
+#### Session Creation
 
 - **Session creation**: client sends `POST /api/v1/session` with a desired
-  nick → server assigns an **auth token** (64 hex characters of
-  cryptographically random bytes) and returns the user ID, nick, and token.
-- The auth token implicitly identifies the client. Clients present it via
-  `Authorization: Bearer <token>`.
-- Anonymous sessions are ephemeral — when the session expires or the user
-  QUITs, the nick is released and there is no way to reclaim it.
+  nick → server sets an **HttpOnly auth cookie** (`neoirc_auth`) containing
+  a cryptographically random token (64 hex characters) and returns the user
+  ID and nick in the JSON response body. No token appears in the JSON body.
+- The auth cookie is HttpOnly, SameSite=Strict, and Secure when behind TLS.
+  Clients never need to handle the token directly — the browser/HTTP client
+  manages cookies automatically.
+- Sessions start anonymous — no password required. When the session expires
+  or the user QUITs, the nick is released.
 
-#### Registered Accounts (Optional)
+#### Setting a Password (Optional, for Multi-Client Access)
 
-For users who want multi-client access (multiple devices sharing one session):
+For users who want to access the same session from multiple devices:
 
-- **Registration**: client sends `POST /api/v1/register` with a nick and
-  password (minimum 8 characters) → server creates a session with the
-  password hashed via bcrypt, and returns the user ID, nick, and auth token.
-- **Login**: client sends `POST /api/v1/login` with nick and password →
-  server verifies the password against the stored bcrypt hash and creates a
-  new client token for the existing session. This enables multi-client
-  access: logging in from a new device adds a client to the existing session
-  rather than creating a new one, so channel memberships and message queues
-  are shared. Note: login only works while the session still exists — if all
-  clients have logged out or the user has sent QUIT, the session is deleted
-  and the registration is lost.
-- Registered accounts cannot be logged into via `POST /api/v1/session` —
-  that endpoint is for anonymous sessions only.
-- Anonymous sessions (created via `/session`) cannot be logged into via
-  `/login` because they have no password set.
+- **Set password via IRC PASS command**: the authenticated client sends
+  `POST /api/v1/messages` with `{"command":"PASS","body":["mypassword"]}`.
+  The server hashes the password with bcrypt and stores it on the session.
+  Password must be at least 8 characters.
+- **Login from another client**: `POST /api/v1/login` with nick and password →
+  server verifies the password, creates a new client for the existing session,
+  and sets an auth cookie. Channel memberships and message queues are shared.
+  Login only works while the session still exists — if all clients have logged
+  out or the user has sent QUIT, the session is deleted and the password is
+  lost.
 
-#### Common Properties (Both Paths)
+#### Common Properties
 
 - Nicks are changeable via the `NICK` command; the server-assigned user ID is
   the stable identity.
 - Server-assigned IDs — clients do not choose their own IDs.
-- Tokens are opaque random bytes, **not JWTs**. No claims, no expiry encoded
-  in the token, no client-side decode. The server is the sole authority on
-  token validity.
+- Auth cookies contain opaque random bytes, **not JWTs**. No claims, no expiry
+  encoded in the token, no client-side decode. The server is the sole authority
+  on cookie validity.
 
 **Rationale:** IRC has no accounts. You connect, pick a nick, and talk.
 Anonymous sessions preserve that simplicity — instant access, zero friction.
 But some users want to access the same session from multiple devices without
-a bouncer. Optional registration with password enables multi-client login
-without adding friction for casual users: if you don't want an account,
-don't create one. Note: in the current implementation, both anonymous and
-registered sessions are deleted when the last client disconnects (QUIT or
-logout); registration does not make a session survive all-client
-removal. Identity verification at the message layer via cryptographic
-signatures (see [Security Model](#security-model)) remains independent
-of account registration.
+a bouncer. The PASS command enables multi-client login without adding friction
+for casual users: if you don't need multi-client, just create a session and
+go. Cookie-based auth eliminates token management from client code entirely —
+browsers and HTTP cookie jars handle it automatically. Note: both anonymous
+and password-protected sessions are deleted when the last client disconnects
+(QUIT or logout). Identity verification at the message layer via cryptographic
+signatures (see [Security Model](#security-model)) remains independent of
+password status.
 
 ### Nick Semantics
 
@@ -232,7 +228,7 @@ A single user session can have multiple clients (phone, laptop, terminal).
 - The server fans out all S2C messages to every active client queue for that
   user session.
 - `GET /api/v1/messages` delivers from the calling client's specific queue,
-  identified by the auth token.
+  identified by the auth cookie.
 - Client queues have **independent expiry/pruning** — one client going offline
   doesn't affect others.
 
@@ -244,11 +240,10 @@ User Session
 ```
 
 **Multi-client via login:** The `POST /api/v1/login` endpoint adds a new
-client to an existing registered session, enabling true multi-client support
-(multiple tokens sharing one nick/session with independent message queues).
-Anonymous sessions created via `POST /api/v1/session` always create a new
-user with a new nick. A future endpoint to "add a client to an existing
-anonymous session" is planned but not yet implemented.
+client to an existing session (one that has a password set via PASS command),
+enabling true multi-client support (multiple cookies sharing one nick/session
+with independent message queues). Sessions without a password cannot be
+logged into.
 
 **Rationale:** The fundamental IRC mobile problem is that you can't have your
 phone and laptop connected simultaneously without a bouncer. Server-side
@@ -301,8 +296,8 @@ The server implements HTTP long-polling for real-time message delivery:
    - The client disconnects (connection closed, no response needed)
 
 **Implementation detail:** The server maintains an in-memory broker with
-per-user notification channels. When a message is enqueued for a user, the
-broker closes all waiting channels for that user, waking up any blocked
+per-client notification channels. When a message is enqueued for a client, the
+broker closes all waiting channels for that client, waking up any blocked
 long-poll handlers. This is O(1) notification — no polling loops, no database
 scanning.
 
@@ -355,19 +350,22 @@ over binary is measured in bytes per message, not meaningful bandwidth. The
 canonicalization story (RFC 8785 JCS) is also well-defined for JSON, which
 matters for signing.
 
-### Why Opaque Tokens Instead of JWTs
+### Why Opaque Cookies Instead of JWTs
 
 JWTs encode claims that clients can decode and potentially rely on. This
 creates a coupling between token format and client behavior. If the server
 needs to revoke a token, change the expiry model, or add/remove claims, JWT
 clients may break or behave incorrectly.
 
-Opaque tokens are simpler:
-- Server generates 32 random bytes → hex-encodes → stores SHA-256 hash
-- Client presents the raw token; server hashes and looks it up
-- Revocation is a database delete
+Opaque auth cookies are simpler:
+- Server generates 32 random bytes → hex-encodes → stores SHA-256 hash →
+  sets raw hex as an HttpOnly cookie
+- On each request, server hashes the cookie value and looks it up
+- Revocation is a database delete (cookie becomes invalid immediately)
 - No clock skew issues, no algorithm confusion, no "none" algorithm attacks
-- Token format can change without breaking clients
+- Cookie format can change without breaking clients
+- Clients never handle tokens directly — browsers and HTTP cookie jars
+  manage everything automatically
 
 ---
 
@@ -391,17 +389,18 @@ The entire read/write loop for a client is two endpoints. Everything else
 
 ### Session Lifecycle
 
-#### Anonymous Session
+#### Session Creation
 
 ```
 ┌─ Client ──────────────────────────────────────────────────┐
 │                                                            │
 │  1. POST /api/v1/session {"nick":"alice"}                  │
-│     → {"id":1, "nick":"alice", "token":"a1b2c3..."}       │
+│     → Set-Cookie: neoirc_auth=<token>; HttpOnly; ...       │
+│     → {"id":1, "nick":"alice"}                             │
 │                                                            │
 │  2. POST /api/v1/messages {"command":"JOIN","to":"#gen"}   │
 │     → {"status":"joined","channel":"#general"}             │
-│     (Server fans out JOIN event to all #general members)   │
+│     (Cookie sent automatically on all subsequent requests) │
 │                                                            │
 │  3. POST /api/v1/messages {"command":"PRIVMSG",            │
 │       "to":"#general","body":["hello"]}                    │
@@ -418,31 +417,37 @@ The entire read/write loop for a client is two endpoints. Everything else
 │  6. POST /api/v1/messages {"command":"QUIT"}               │
 │     → {"status":"quit"}                                    │
 │     (Server broadcasts QUIT, removes from channels,        │
-│      deletes session, releases nick)                       │
+│      deletes session, releases nick, clears cookie)        │
 │                                                            │
 └────────────────────────────────────────────────────────────┘
 ```
 
-#### Registered Account
+#### Multi-Client via Password
 
 ```
-┌─ Client ──────────────────────────────────────────────────┐
+┌─ Client A ────────────────────────────────────────────────┐
 │                                                            │
-│  1. POST /api/v1/register                                  │
-│     {"nick":"alice", "password":"s3cret!!"}                │
-│     → {"id":1, "nick":"alice", "token":"a1b2c3..."}       │
-│     (Session created with bcrypt-hashed password)          │
+│  1. POST /api/v1/session {"nick":"alice"}                  │
+│     → Set-Cookie: neoirc_auth=<token_a>; HttpOnly; ...     │
+│     → {"id":1, "nick":"alice"}                             │
+│                                                            │
+│  2. POST /api/v1/messages                                  │
+│     {"command":"PASS","body":["s3cret!!"]}                 │
+│     → {"status":"ok"}                                      │
+│     (Password set via IRC PASS command)                    │
 │                                                            │
 │  ... use the API normally (JOIN, PRIVMSG, poll, etc.) ...  │
 │                                                            │
-│  (From another device, while session is still active)      │
+└────────────────────────────────────────────────────────────┘
+
+┌─ Client B (another device, while session is still active) ┐
 │                                                            │
-│  2. POST /api/v1/login                                     │
+│  3. POST /api/v1/login                                     │
 │     {"nick":"alice", "password":"s3cret!!"}                │
-│     → {"id":1, "nick":"alice", "token":"d4e5f6..."}       │
+│     → Set-Cookie: neoirc_auth=<token_b>; HttpOnly; ...     │
+│     → {"id":1, "nick":"alice"}                             │
 │     (New client added to existing session — channels       │
-│      and message queues are preserved. If all clients      │
-│      have logged out, session no longer exists.)           │
+│      and message queues are preserved.)                    │
 │                                                            │
 └────────────────────────────────────────────────────────────┘
 ```
@@ -460,28 +465,28 @@ The entire read/write loop for a client is two endpoints. Everything else
               │              │              │
     ┌─────────▼──┐  ┌───────▼────┐  ┌──────▼─────┐
     │client_queue│  │client_queue│  │client_queue│
-    │ user_id=1  │  │ user_id=2  │  │ user_id=3  │
+    │ client_id=1│  │ client_id=2│  │ client_id=3│
     │ msg_id=N   │  │ msg_id=N   │  │ msg_id=N   │
     └────────────┘  └────────────┘  └────────────┘
          alice           bob             carol
 
-Each message is stored ONCE. One queue entry per recipient.
+Each message is stored ONCE. One queue entry per recipient client.
 ```
 
-The `client_queues` table contains `(user_id, message_id)` pairs. When a
+The `client_queues` table contains `(client_id, message_id)` pairs. When a
 client polls with `GET /messages?after=<queue_id>`, the server queries for
-queue entries with `id > after` for that user, joins against the messages
+queue entries with `id > after` for that client, joins against the messages
 table, and returns the results. The `queue_id` (auto-incrementing primary
 key of `client_queues`) serves as a monotonically increasing cursor.
 
 ### In-Memory Broker
 
 The server maintains an in-memory notification broker to avoid database
-polling. The broker is a map of `user_id → []chan struct{}`. When a message
-is enqueued for a user:
+polling. The broker is a map of `client_id → []chan struct{}`. When a message
+is enqueued for a client:
 
-1. The handler calls `broker.Notify(userID)`
-2. The broker closes all waiting channels for that user
+1. The handler calls `broker.Notify(clientID)`
+2. The broker closes all waiting channels for that client
 3. Any goroutines blocked in `select` on those channels wake up
 4. The woken handler queries the database for new queue entries
 5. Messages are returned to the client
@@ -523,7 +528,7 @@ the same JSON envelope:
 | `params`  | array of strings    | Sometimes | Sometimes | Additional IRC-style positional parameters. Used by commands like `MODE`, `KICK`, and numeric replies like `353` (NAMES). |
 | `body`    | array or object     | Usually   | Usually   | Structured message body. For text messages: array of strings (one per line). For structured data (e.g., `PUBKEY`): JSON object. **Never a raw string.** |
 | `ts`      | string (ISO 8601)   | Ignored   | Always    | Server-assigned timestamp in RFC 3339 / ISO 8601 format with nanosecond precision. Example: `"2026-02-10T20:00:00.000000000Z"`. Always UTC. |
-| `meta`    | object              | Optional  | If present | Extensible metadata. Used for cryptographic signatures (`meta.sig`, `meta.alg`), content hashes, or any client-defined key/value pairs. Server relays `meta` verbatim — it does not interpret or validate it. |
+| `meta`    | object              | Optional  | If present | Extensible metadata. Used for cryptographic signatures (`meta.sig`, `meta.alg`), hashcash proof-of-work (`meta.hashcash`), content hashes, or any client-defined key/value pairs. Server relays `meta` verbatim except for `hashcash` which is validated on channels with `+H` mode. |
 
 **Important invariants:**
 
@@ -729,6 +734,35 @@ Change the user's nickname.
 
 **IRC reference:** RFC 1459 §4.1.2
 
+#### PASS — Set Session Password
+
+Set a password on the current session, enabling multi-client login via
+`POST /api/v1/login`. The password is hashed with bcrypt and stored
+server-side.
+
+**C2S:**
+```json
+{"command": "PASS", "body": ["mypassword"]}
+```
+
+**Behavior:**
+
+- `body[0]` is the password. Must be at least 8 characters.
+- On success, the server responds with `{"status": "ok"}`.
+- If the password is too short or missing, the server sends
+  ERR_NEEDMOREPARAMS (461) via the message queue.
+- Calling PASS again overwrites the previous password.
+- Once a password is set, `POST /api/v1/login` can be used with the nick
+  and password to create additional clients on the same session.
+
+**Response:** `200 OK`
+```json
+{"status": "ok"}
+```
+
+**IRC reference:** Inspired by RFC 1459 §4.1.1 (PASS), repurposed for
+session password management.
+
 #### TOPIC — Set Channel Topic
 
 Set or change a channel's topic.
@@ -795,7 +829,7 @@ Destroy the session and disconnect from the server.
   quitting user. The quitting user does **not** receive their own QUIT.
 - The user is removed from all channels.
 - Empty channels are deleted (ephemeral).
-- The user's session is destroyed — the auth token is invalidated, the nick
+- The user's session is destroyed — the auth cookie is invalidated, the nick
   is released.
 - Subsequent requests with the old token return HTTP 401.
 
@@ -1013,12 +1047,13 @@ carries IRC-style parameters (e.g., channel name, target nick).
 Inspired by IRC, simplified:
 
 | Mode | Name           | Meaning |
-|------|--------------|---------|
+|------|----------------|---------|
 | `+i` | Invite-only    | Only invited users can join |
 | `+m` | Moderated      | Only voiced (`+v`) users and operators (`+o`) can send |
 | `+s` | Secret         | Channel hidden from LIST response |
 | `+t` | Topic lock     | Only operators can change the topic |
 | `+n` | No external    | Only channel members can send messages to the channel |
+| `+H` | Hashcash       | Requires proof-of-work for PRIVMSG (parameter: bits, e.g. `+H 20`) |
 
 **User channel modes (set per-user per-channel):**
 
@@ -1029,14 +1064,64 @@ Inspired by IRC, simplified:
 
 **Status:** Channel modes are defined but not yet enforced. The `modes` column
 exists in the channels table but the server does not check modes on actions.
+Exception: `+H` (hashcash) is fully enforced — see below.
+
+### Per-Channel Hashcash (Anti-Spam)
+
+Channels can require hashcash proof-of-work for every `PRIVMSG`. This is an
+anti-spam mechanism: channel operators set a difficulty level, and clients must
+compute a proof-of-work stamp bound to the specific channel and message before
+sending.
+
+**Setting the requirement:**
+
+```
+MODE #channel +H <bits>    — require <bits> leading zero bits (1-40)
+MODE #channel -H           — disable hashcash requirement
+```
+
+**Stamp format:** `1:bits:YYMMDD:channel:bodyhash:counter`
+
+- `bits` — difficulty (leading zero bits in SHA-256 hash of the stamp)
+- `YYMMDD` — current date (prevents old token reuse)
+- `channel` — channel name (prevents cross-channel reuse)
+- `bodyhash` — hex-encoded SHA-256 of the message body (binds stamp to message)
+- `counter` — hex nonce
+
+**Sending a message to a hashcash-protected channel:**
+
+Include the hashcash stamp in the `meta` field:
+
+```json
+{
+  "command": "PRIVMSG",
+  "to": "#general",
+  "body": ["hello world"],
+  "meta": {
+    "hashcash": "1:20:260317:#general:a1b2c3...bodyhash:1f4a"
+  }
+}
+```
+
+**Server validation:** The server checks that the stamp is well-formed, meets
+the required difficulty, is bound to the correct channel and message body, has a
+recent date, and has not been previously used. Spent stamps are cached for 1
+year to prevent replay attacks.
+
+**Error responses:** If the channel requires hashcash and the stamp is missing,
+invalid, or replayed, the server returns `ERR_CANNOTSENDTOCHAN (404)` with a
+descriptive reason.
+
+**Client minting:** The CLI provides `MintChannelHashcash(bits, channel, body)`
+to compute stamps. Higher bit counts take exponentially longer to compute.
 
 ---
 
 ## API Reference
 
 All endpoints accept and return `application/json`. Authenticated endpoints
-require `Authorization: Bearer <token>` header. The token is obtained from
-`POST /api/v1/session`.
+require the `neoirc_auth` cookie, which is set automatically by
+`POST /api/v1/session` and `POST /api/v1/login`.
 
 All API responses include appropriate HTTP status codes. Error responses have
 the format:
@@ -1065,11 +1150,18 @@ difficulty is advertised via `GET /api/v1/server` in the `hashcash_bits` field.
 | `pow_token` | string | Conditional | Hashcash stamp (required when server has `hashcash_bits` > 0) |
 
 **Response:** `201 Created`
+
+The response sets an `neoirc_auth` HttpOnly cookie containing the auth token.
+The JSON body does **not** include the token.
+
+```
+Set-Cookie: neoirc_auth=494ba9fc...e3; Path=/; HttpOnly; SameSite=Strict
+```
+
 ```json
 {
   "id": 1,
-  "nick": "alice",
-  "token": "494ba9fc0f2242873fc5c285dd4a24fc3844ba5e67789a17e69b6fe5f8c132e3"
+  "nick": "alice"
 }
 ```
 
@@ -1077,7 +1169,16 @@ difficulty is advertised via `GET /api/v1/server` in the `hashcash_bits` field.
 |---------|---------|-------------|
 | `id`    | integer | Server-assigned user ID |
 | `nick`  | string  | Confirmed nick (always matches request on success) |
-| `token` | string  | 64-character hex auth token. Store this — it's the only credential. |
+
+**Cookie properties:**
+
+| Property   | Value |
+|------------|-------|
+| `Name`     | `neoirc_auth` |
+| `HttpOnly` | `true` (not accessible from JavaScript) |
+| `SameSite` | `Strict` (prevents CSRF) |
+| `Secure`   | `true` when behind TLS |
+| `Path`     | `/` |
 
 **Errors:**
 
@@ -1090,66 +1191,18 @@ difficulty is advertised via `GET /api/v1/server` in the `hashcash_bits` field.
 
 **curl example:**
 ```bash
-TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/session \
+# Use -c to save cookies, -b to send them
+curl -s -c cookies.txt -X POST http://localhost:8080/api/v1/session \
   -H 'Content-Type: application/json' \
-  -d '{"nick":"alice","pow_token":"1:20:260310:neoirc::3a2f1"}' | jq -r .token)
-echo $TOKEN
-```
-
-### POST /api/v1/register — Register Account
-
-Create a new user session with a password. The password is hashed
-with bcrypt and stored server-side. The password enables login from
-additional clients via `POST /api/v1/login` while the session
-remains active.
-
-**Request Body:**
-```json
-{"nick": "alice", "password": "mypassword"}
-```
-
-| Field      | Type   | Required | Constraints |
-|------------|--------|----------|-------------|
-| `nick`     | string | Yes      | 1–32 characters, must be unique on the server |
-| `password` | string | Yes      | Minimum 8 characters |
-
-**Response:** `201 Created`
-```json
-{
-  "id": 1,
-  "nick": "alice",
-  "token": "494ba9fc0f2242873fc5c285dd4a24fc3844ba5e67789a17e69b6fe5f8c132e3"
-}
-```
-
-| Field   | Type    | Description |
-|---------|---------|-------------|
-| `id`    | integer | Server-assigned user ID |
-| `nick`  | string  | Confirmed nick |
-| `token` | string  | 64-character hex auth token |
-
-**Errors:**
-
-| Status | Error | When |
-|--------|-------|------|
-| 400    | `invalid nick format` | Nick doesn't match allowed format |
-| 400    | `password must be at least 8 characters` | Password too short |
-| 409    | `nick already taken` | Another active session holds this nick |
-
-**curl example:**
-```bash
-TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/register \
-  -H 'Content-Type: application/json' \
-  -d '{"nick":"alice","password":"mypassword"}' | jq -r .token)
-echo $TOKEN
+  -d '{"nick":"alice","pow_token":"1:20:260310:neoirc::3a2f1"}'
 ```
 
 ### POST /api/v1/login — Login to Account
 
-Authenticate with a previously registered nick and password. Creates a new
-client token for the existing session, preserving channel memberships and
-message queues. This is how multi-client access works for registered accounts:
-each login adds a new client to the session.
+Authenticate with a nick and password (set via the PASS IRC command). Creates a
+new client for the existing session, preserving channel memberships and message
+queues. This is how multi-client access works: each login adds a new client to
+the session with its own auth cookie and message delivery queue.
 
 On successful login, the server enqueues MOTD messages and synthetic channel
 state (JOIN + TOPIC + NAMES for each channel the session belongs to) into the
@@ -1162,37 +1215,37 @@ new client's queue, so the client can immediately restore its UI state.
 
 | Field      | Type   | Required | Constraints |
 |------------|--------|----------|-------------|
-| `nick`     | string | Yes      | Must match a registered account |
-| `password` | string | Yes      | Must match the account's password |
+| `nick`     | string | Yes      | Must match an active session with a password set |
+| `password` | string | Yes      | Must match the session's password |
 
 **Response:** `200 OK`
+
+The response sets an `neoirc_auth` HttpOnly cookie for the new client.
+
 ```json
 {
   "id": 1,
-  "nick": "alice",
-  "token": "7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f"
+  "nick": "alice"
 }
 ```
 
 | Field   | Type    | Description |
 |---------|---------|-------------|
-| `id`    | integer | Session ID (same as when registered) |
+| `id`    | integer | Session ID |
 | `nick`  | string  | Current nick |
-| `token` | string  | New 64-character hex auth token for this client |
 
 **Errors:**
 
 | Status | Error | When |
 |--------|-------|------|
 | 400    | `nick and password required` | Missing nick or password |
-| 401    | `invalid credentials` | Wrong password, nick not found, or account has no password |
+| 401    | `invalid credentials` | Wrong password, nick not found, or session has no password set |
 
 **curl example:**
 ```bash
-TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/login \
+curl -s -c cookies.txt -X POST http://localhost:8080/api/v1/login \
   -H 'Content-Type: application/json' \
-  -d '{"nick":"alice","password":"mypassword"}' | jq -r .token)
-echo $TOKEN
+  -d '{"nick":"alice","password":"mypassword"}'
 ```
 
 ### GET /api/v1/state — Get Session State
@@ -1236,13 +1289,13 @@ Each channel object:
 **curl example:**
 ```bash
 curl -s http://localhost:8080/api/v1/state \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 ```
 
 **Reconnect with channel state initialization:**
 ```bash
 curl -s "http://localhost:8080/api/v1/state?initChannelState=1" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 ```
 
 ### GET /api/v1/messages — Poll Messages (Long-Poll)
@@ -1302,14 +1355,12 @@ real-time endpoint — clients call it in a loop.
 
 **curl example (immediate):**
 ```bash
-curl -s "http://localhost:8080/api/v1/messages?after=0&timeout=0" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+curl -s -b cookies.txt "http://localhost:8080/api/v1/messages?after=0&timeout=0" | jq .
 ```
 
 **curl example (long-poll, 15s):**
 ```bash
-curl -s "http://localhost:8080/api/v1/messages?after=42&timeout=15" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+curl -s -b cookies.txt "http://localhost:8080/api/v1/messages?after=42&timeout=15" | jq .
 ```
 
 ### POST /api/v1/messages — Send Command
@@ -1336,6 +1387,7 @@ reference with all required and optional fields.
 | `JOIN`    | `to`                |               | 200 OK          |
 | `PART`    | `to`                | `body`        | 200 OK          |
 | `NICK`    | `body`              |               | 200 OK          |
+| `PASS`    | `body`              |               | 200 OK          |
 | `TOPIC`   | `to`, `body`        |               | 200 OK          |
 | `MODE`    | `to`                |               | 200 OK          |
 | `NAMES`   | `to`                |               | 200 OK          |
@@ -1350,14 +1402,14 @@ All IRC commands return HTTP 200 OK. IRC-level success and error responses
 are delivered as **numeric replies** through the message queue (see
 [Numeric Replies](#numeric-replies) below). HTTP error codes (4xx/5xx) are
 reserved for transport-level problems: malformed JSON (400), missing/invalid
-auth tokens (401), and server errors (500).
+auth cookies (401), and server errors (500).
 
 **HTTP errors (transport-level only):**
 
 | Status | Error | When |
 |--------|-------|------|
 | 400    | `invalid request` | Malformed JSON or empty command |
-| 401    | `unauthorized` | Missing or invalid auth token |
+| 401    | `unauthorized` | Missing or invalid auth cookie |
 | 500    | `internal error` | Server-side failure |
 
 **IRC numeric error replies (delivered via message queue):**
@@ -1448,11 +1500,11 @@ events). Event messages are delivered via the live queue only.
 ```bash
 # Latest 50 messages in #general
 curl -s "http://localhost:8080/api/v1/history?target=%23general&limit=50" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 
 # Older messages (pagination)
 curl -s "http://localhost:8080/api/v1/history?target=%23general&before=100&limit=50" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 ```
 
 ### GET /api/v1/channels — List Channels
@@ -1483,18 +1535,22 @@ List members of a channel. The `{name}` parameter is the channel name
 **curl example:**
 ```bash
 curl -s http://localhost:8080/api/v1/channels/general/members \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 ```
 
 ### POST /api/v1/logout — Logout
 
-Destroy the current client's auth token. If no other clients remain on the
-session, the user is fully cleaned up: parted from all channels (with QUIT
-broadcast to members), session deleted, nick released.
+Destroy the current client's session cookie and server-side client record.
+If no other clients remain on the session, the user is fully cleaned up:
+parted from all channels (with QUIT broadcast to members), session deleted,
+nick released. The auth cookie is cleared in the response.
 
-**Request:** No body. Requires auth.
+**Request:** No body. Requires auth cookie.
 
 **Response:** `200 OK`
+
+The response clears the `neoirc_auth` cookie.
+
 ```json
 {"status": "ok"}
 ```
@@ -1503,12 +1559,11 @@ broadcast to members), session deleted, nick released.
 
 | Status | Error | When |
 |--------|-------|------|
-| 401    | `unauthorized` | Missing or invalid auth token |
+| 401    | `unauthorized` | Missing or invalid auth cookie |
 
 **curl example:**
 ```bash
-curl -s -X POST http://localhost:8080/api/v1/logout \
-  -H "Authorization: Bearer $TOKEN" | jq .
+curl -s -b cookies.txt -c cookies.txt -X POST http://localhost:8080/api/v1/logout | jq .
 ```
 
 ### GET /api/v1/users/me — Current User Info
@@ -1532,7 +1587,7 @@ Return the current user's session state. This is an alias for
 **curl example:**
 ```bash
 curl -s http://localhost:8080/api/v1/users/me \
-  -H "Authorization: Bearer $TOKEN" | jq .
+  -b cookies.txt | jq .
 ```
 
 ### GET /api/v1/server — Server Info
@@ -1777,20 +1832,21 @@ authenticity.
 
 ### Authentication
 
-- **Session auth**: Opaque bearer tokens (64 hex chars = 256 bits of entropy).
-  Tokens are hashed (SHA-256) before storage and validated on every request.
+- **Cookie-based auth**: Opaque HttpOnly cookies (64 hex chars = 256 bits of
+  entropy). Tokens are hashed (SHA-256) before storage and validated on every
+  request. Cookies are HttpOnly (no JavaScript access), SameSite=Strict
+  (CSRF protection), and Secure when behind TLS.
 - **Anonymous sessions**: `POST /api/v1/session` requires only a nick. No
-  password, instant access. The token is the sole credential.
-- **Registered accounts**: `POST /api/v1/register` accepts a nick and password
-  (minimum 8 characters). The password is hashed with bcrypt at the default
-  cost factor and stored alongside the session. `POST /api/v1/login`
-  authenticates against the stored hash and issues a new client token.
+  password, instant access. The auth cookie is the sole credential.
+- **Password-protected sessions**: The PASS IRC command sets a bcrypt-hashed
+  password on the session. `POST /api/v1/login` authenticates against the
+  stored hash and issues a new client cookie.
 - **Password security**: Passwords are never stored in plain text. bcrypt
-  handles salting and key stretching automatically. Anonymous sessions have
-  an empty `password_hash` and cannot be logged into via `/login`.
-- **Token security**: Tokens should be treated like session cookies. Transmit
-  only over HTTPS in production. If a token is compromised, the attacker has
-  full access to the session until QUIT or expiry.
+  handles salting and key stretching automatically. Sessions without a
+  password cannot be logged into via `/login`.
+- **Cookie security**: Auth cookies should only be transmitted over HTTPS in
+  production. If a cookie is compromised, the attacker has full access to the
+  session until QUIT or expiry.
 
 ### Message Integrity
 
@@ -1827,8 +1883,10 @@ authenticity.
 - **HTTPS is strongly recommended** for production deployments. The server
   itself serves plain HTTP — use a reverse proxy (nginx, Caddy, etc.) for TLS
   termination.
-- **CORS**: The server allows all origins by default (`Access-Control-Allow-Origin: *`).
-  Restrict this in production via reverse proxy configuration if needed.
+- **CORS**: The server allows all origins with credentials
+  (`Access-Control-Allow-Credentials: true`), reflecting the request Origin.
+  This enables cookie-based auth from cross-origin clients. Restrict origins
+  in production via reverse proxy configuration if needed.
 - **Content-Security-Policy**: The server sets a strict CSP header on all
   responses, restricting resource loading to same-origin and disabling
   dangerous features (object embeds, framing, base tag injection). The
@@ -1937,7 +1995,7 @@ The database schema is managed via embedded SQL migration files in
 
 #### `sessions`
 | Column          | Type     | Description |
-|----------------|----------|-------------|
+|-----------------|----------|-------------|
 | `id`            | INTEGER  | Primary key (auto-increment) |
 | `uuid`          | TEXT     | Unique session UUID |
 | `nick`          | TEXT     | Unique nick |
@@ -1947,9 +2005,11 @@ The database schema is managed via embedded SQL migration files in
 | `created_at`    | DATETIME | Session creation time |
 | `last_seen`     | DATETIME | Last API request time |
 
+Index on `(uuid)`.
+
 #### `clients`
 | Column       | Type     | Description |
-|-------------|----------|-------------|
+|--------------|----------|-------------|
 | `id`         | INTEGER  | Primary key (auto-increment) |
 | `uuid`       | TEXT     | Unique client UUID |
 | `session_id` | INTEGER  | FK → sessions.id (cascade delete) |
@@ -1957,24 +2017,28 @@ The database schema is managed via embedded SQL migration files in
 | `created_at` | DATETIME | Client creation time |
 | `last_seen`  | DATETIME | Last API request time |
 
+Indexes on `(token)` and `(session_id)`.
+
 #### `channels`
 | Column        | Type     | Description |
-|-------------|----------|-------------|
+|---------------|----------|-------------|
 | `id`          | INTEGER  | Primary key (auto-increment) |
 | `name`        | TEXT     | Unique channel name (e.g., `#general`) |
 | `topic`       | TEXT     | Channel topic (default empty) |
+| `topic_set_by`| TEXT     | Nick of the user who set the topic (default empty) |
+| `topic_set_at`| DATETIME | When the topic was last set |
 | `created_at`  | DATETIME | Channel creation time |
 | `updated_at`  | DATETIME | Last modification time |
 
 #### `channel_members`
 | Column       | Type     | Description |
-|-------------|----------|-------------|
+|--------------|----------|-------------|
 | `id`         | INTEGER  | Primary key (auto-increment) |
-| `channel_id`| INTEGER  | FK → channels.id |
-| `user_id`   | INTEGER  | FK → users.id |
+| `channel_id` | INTEGER  | FK → channels.id (cascade delete) |
+| `session_id` | INTEGER  | FK → sessions.id (cascade delete) |
 | `joined_at`  | DATETIME | When the user joined |
 
-Unique constraint on `(channel_id, user_id)`.
+Unique constraint on `(channel_id, session_id)`.
 
 #### `messages`
 | Column      | Type     | Description |
@@ -1984,6 +2048,7 @@ Unique constraint on `(channel_id, user_id)`.
 | `command`   | TEXT     | IRC command (`PRIVMSG`, `JOIN`, etc.) |
 | `msg_from`  | TEXT     | Sender nick |
 | `msg_to`    | TEXT     | Target (`#channel` or nick) |
+| `params`    | TEXT     | JSON-encoded IRC-style positional parameters |
 | `body`      | TEXT     | JSON-encoded body (array or object) |
 | `meta`      | TEXT     | JSON-encoded metadata |
 | `created_at`| DATETIME | Server timestamp |
@@ -1994,11 +2059,11 @@ Indexes on `(msg_to, id)` and `(created_at)`.
 | Column      | Type     | Description |
 |-------------|----------|-------------|
 | `id`        | INTEGER  | Primary key (auto-increment). Used as the poll cursor. |
-| `user_id`   | INTEGER  | FK → users.id |
-| `message_id`| INTEGER  | FK → messages.id |
+| `client_id` | INTEGER  | FK → clients.id (cascade delete) |
+| `message_id`| INTEGER  | FK → messages.id (cascade delete) |
 | `created_at`| DATETIME | When the entry was queued |
 
-Unique constraint on `(user_id, message_id)`. Index on `(user_id, id)`.
+Unique constraint on `(client_id, message_id)`. Index on `(client_id, id)`.
 
 The `client_queues.id` is the monotonically increasing cursor used by
 `GET /messages?after=<id>`. This is more reliable than timestamps (no clock
@@ -2011,7 +2076,7 @@ skew issues) and simpler than UUIDs (integer comparison vs. string comparison).
 - **Client output queue entries**: Pruned automatically when older than
   `QUEUE_MAX_AGE` (default 30 days).
 - **Channels**: Deleted when the last member leaves (ephemeral).
-- **Sessions**: Both anonymous and registered sessions are deleted on `QUIT`
+- **Sessions**: Both anonymous and password-protected sessions are deleted on `QUIT`
   or when the last client logs out (`POST /api/v1/logout` with no remaining
   clients triggers session cleanup). There is no distinction between session
   types in the cleanup path — `handleQuit` and `cleanupUser` both call
@@ -2172,68 +2237,59 @@ A complete client needs only four HTTP calls:
 ### Step-by-Step with curl
 
 ```bash
-# 1a. Create an anonymous session (no account)
-export TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/session \
+# 1a. Create a session (cookie saved automatically with -c)
+curl -s -c cookies.txt -X POST http://localhost:8080/api/v1/session \
   -H 'Content-Type: application/json' \
-  -d '{"nick":"testuser"}' | jq -r .token)
+  -d '{"nick":"testuser"}'
 
-# 1b. Or register an account (multi-client support)
-export TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/register \
+# 1b. Optionally set a password for multi-client access
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
-  -d '{"nick":"testuser","password":"mypassword"}' | jq -r .token)
+  -d '{"command":"PASS","body":["mypassword"]}'
 
-# 1c. Or login to an existing account
-export TOKEN=$(curl -s -X POST http://localhost:8080/api/v1/login \
+# 1c. Login from another device (saves new cookie)
+curl -s -c cookies2.txt -X POST http://localhost:8080/api/v1/login \
   -H 'Content-Type: application/json' \
-  -d '{"nick":"testuser","password":"mypassword"}' | jq -r .token)
+  -d '{"nick":"testuser","password":"mypassword"}'
 
 # 2. Join a channel
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"JOIN","to":"#general"}'
 
 # 3. Send a message
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"PRIVMSG","to":"#general","body":["hello from curl!"]}'
 
 # 4. Poll for messages (one-shot)
-curl -s "http://localhost:8080/api/v1/messages?after=0&timeout=0" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+curl -s -b cookies.txt "http://localhost:8080/api/v1/messages?after=0&timeout=0" | jq .
 
 # 5. Long-poll (blocks up to 15s waiting for messages)
-curl -s "http://localhost:8080/api/v1/messages?after=0&timeout=15" \
-  -H "Authorization: Bearer $TOKEN" | jq .
+curl -s -b cookies.txt "http://localhost:8080/api/v1/messages?after=0&timeout=15" | jq .
 
 # 6. Send a DM
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"PRIVMSG","to":"othernick","body":["hey!"]}'
 
 # 7. Change nick
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"NICK","body":["newnick"]}'
 
 # 8. Set channel topic
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"TOPIC","to":"#general","body":["New topic!"]}'
 
 # 9. Leave a channel
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"PART","to":"#general","body":["goodbye"]}'
 
 # 10. Disconnect
-curl -s -X POST http://localhost:8080/api/v1/messages \
-  -H "Authorization: Bearer $TOKEN" \
+curl -s -b cookies.txt -X POST http://localhost:8080/api/v1/messages \
   -H 'Content-Type: application/json' \
   -d '{"command":"QUIT","body":["leaving"]}'
 ```
@@ -2243,27 +2299,25 @@ curl -s -X POST http://localhost:8080/api/v1/messages \
 The key to real-time messaging is the poll loop. Here's the pattern:
 
 ```python
-# Python example
-import requests, json
+# Python example — using requests.Session for automatic cookie handling
+import requests, json, time
 
 BASE = "http://localhost:8080/api/v1"
-token = None
+session = requests.Session()  # Manages cookies automatically
 last_id = 0
 
-# Create session
-resp = requests.post(f"{BASE}/session", json={"nick": "pybot"})
-token = resp.json()["token"]
-headers = {"Authorization": f"Bearer {token}"}
+# Create session (cookie set automatically via Set-Cookie header)
+resp = session.post(f"{BASE}/session", json={"nick": "pybot"})
+print(f"Session: {resp.json()}")
 
 # Join channel
-requests.post(f"{BASE}/messages", headers=headers,
+session.post(f"{BASE}/messages",
              json={"command": "JOIN", "to": "#general"})
 
 # Poll loop
 while True:
     try:
-        resp = requests.get(f"{BASE}/messages",
-                          headers=headers,
+        resp = session.get(f"{BASE}/messages",
                           params={"after": last_id, "timeout": 15},
                           timeout=20)  # HTTP timeout > long-poll timeout
         data = resp.json()
@@ -2280,14 +2334,14 @@ while True:
 ```
 
 ```javascript
-// JavaScript/browser example
-async function pollLoop(token) {
+// JavaScript/browser example — cookies sent automatically
+async function pollLoop() {
   let lastId = 0;
   while (true) {
     try {
       const resp = await fetch(
         `/api/v1/messages?after=${lastId}&timeout=15`,
-        {headers: {'Authorization': `Bearer ${token}`}}
+        {credentials: 'same-origin'}  // Include cookies
       );
       if (resp.status === 401) { /* session expired */ break; }
       const data = await resp.json();
@@ -2319,8 +2373,8 @@ Clients should handle these message commands from the queue:
 
 ### Error Handling
 
-- **HTTP 401**: Token expired or invalid. Re-create session (anonymous) or
-  re-login (registered account).
+- **HTTP 401**: Auth cookie expired or invalid. Re-create session or
+  re-login (if a password was set).
 - **HTTP 404**: Channel or user not found.
 - **HTTP 409**: Nick already taken (on session creation, registration, or
   NICK change).
@@ -2340,10 +2394,11 @@ Clients should handle these message commands from the queue:
 4. **DM tab logic**: When you receive a PRIVMSG where `to` is not a channel
    (no `#` prefix), the DM tab should be keyed by the **other** user's nick:
    if `from` is you, use `to`; if `from` is someone else, use `from`.
-5. **Reconnection**: If the poll loop fails with 401, the token is invalid.
-   For anonymous sessions, create a new session. For registered accounts,
-   log in again via `POST /api/v1/login` to get a fresh token on the same
-   session. If it fails with a network error, retry with backoff.
+5. **Reconnection**: If the poll loop fails with 401, the auth cookie is
+   invalid. For sessions without a password, create a new session. For
+   sessions with a password set (via PASS command), log in again via
+   `POST /api/v1/login` to get a fresh cookie on the same session. If it
+   fails with a network error, retry with backoff.
 
 ---
 
@@ -2502,8 +2557,10 @@ creating one session pays once and keeps their session.
   331-332 TOPIC, 352-353 WHO/NAMES, 366, 372-376 MOTD, 401-461 errors)
 - [ ] **Max message size enforcement** — reject oversized messages
 - [ ] **NOTICE command** — distinct from PRIVMSG (no auto-reply flag)
-- [ ] **Multi-client sessions** — add client to existing session
-  (share nick across devices)
+- [x] **Multi-client sessions** — set a password via PASS command, then
+  login from additional devices via `POST /api/v1/login`
+- [x] **Cookie-based auth** — HttpOnly cookies replace Bearer tokens for
+  all API authentication
 
 ### Future (1.0+)
 
@@ -2616,13 +2673,12 @@ neoirc/
    build a working IRC-style TUI client against this API in an afternoon, the
    API is too complex.
 
-2. **Accounts optional** — anonymous sessions are instant: pick a nick and
+2. **Passwords optional** — anonymous sessions are instant: pick a nick and
    talk. No registration, no email verification. The cost of entry is a
    hashcash proof, not bureaucracy. For users who want multi-client access
-   (multiple devices sharing one session), optional account registration
-   with password is available — but never required. Identity
-   verification at the message layer uses cryptographic signing,
-   independent of account status.
+   (multiple devices sharing one session), the PASS command sets a password
+   on the session — but it's never required. Identity verification at the
+   message layer uses cryptographic signing, independent of password status.
 
 3. **IRC semantics over HTTP** — command names and numeric codes from
    RFC 1459/2812. If you've built an IRC client or bot, you already know the

internal/cli/api/client.go

@@ -9,6 +9,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	"net/http/cookiejar"
 	"net/url"
 	"strconv"
 	"strings"
@@ -28,16 +29,19 @@ var errHTTP = errors.New("HTTP error")
 // Client wraps HTTP calls to the neoirc server API.
 type Client struct {
 	BaseURL    string
-	Token      string
 	HTTPClient *http.Client
 }
 
-// NewClient creates a new API client.
+// NewClient creates a new API client with a cookie jar
+// for automatic auth cookie management.
 func NewClient(baseURL string) *Client {
-	return &Client{ //nolint:exhaustruct // Token set after CreateSession
+	jar, _ := cookiejar.New(nil)
+
+	return &Client{
 		BaseURL: baseURL,
 		HTTPClient: &http.Client{ //nolint:exhaustruct // defaults fine
 			Timeout: httpTimeout,
+			Jar:     jar,
 		},
 	}
 }
@@ -79,8 +83,6 @@ func (client *Client) CreateSession(
 		return nil, fmt.Errorf("decode session: %w", err)
 	}
 
-	client.Token = resp.Token
-
 	return &resp, nil
 }
 
@@ -121,6 +123,7 @@ func (client *Client) PollMessages(
 		Timeout: time.Duration(
 			timeout+pollExtraTime,
 		) * time.Second,
+		Jar: client.HTTPClient.Jar,
 	}
 
 	params := url.Values{}
@@ -145,10 +148,6 @@ func (client *Client) PollMessages(
 		return nil, fmt.Errorf("new request: %w", err)
 	}
 
-	request.Header.Set(
-		"Authorization", "Bearer "+client.Token,
-	)
-
 	resp, err := pollClient.Do(request)
 	if err != nil {
 		return nil, fmt.Errorf("poll request: %w", err)
@@ -304,12 +303,6 @@ func (client *Client) do(
 		"Content-Type", "application/json",
 	)
 
-	if client.Token != "" {
-		request.Header.Set(
-			"Authorization", "Bearer "+client.Token,
-		)
-	}
-
 	resp, err := client.HTTPClient.Do(request)
 	if err != nil {
 		return nil, fmt.Errorf("http: %w", err)

internal/cli/api/hashcash.go

@@ -7,6 +7,8 @@ import (
 	"fmt"
 	"math/big"
 	"time"
+
+	"git.eeqj.de/sneak/neoirc/internal/hashcash"
 )
 
 const (
@@ -37,6 +39,23 @@ func MintHashcash(bits int, resource string) string {
 	}
 }
 
+// MintChannelHashcash computes a hashcash stamp bound to
+// a specific channel and message body. The stamp format
+// is 1:bits:YYMMDD:channel:bodyhash:counter where
+// bodyhash is the hex-encoded SHA-256 of the message
+// body bytes. Delegates to the internal/hashcash package.
+func MintChannelHashcash(
+	bits int,
+	channel string,
+	body []byte,
+) string {
+	bodyHash := hashcash.BodyHash(body)
+
+	return hashcash.MintChannelStamp(
+		bits, channel, bodyHash,
+	)
+}
+
 // hasLeadingZeroBits checks if hash has at least numBits
 // leading zero bits.
 func hasLeadingZeroBits(

internal/cli/api/types.go

@@ -12,7 +12,6 @@ type SessionRequest struct {
 type SessionResponse struct {
 	ID   int64  `json:"id"`
 	Nick string `json:"nick"`
-	Token string `json:"token"`
 }
 
 // StateResponse is the response from GET /api/v1/state.

internal/db/auth.go

@@ -16,80 +16,28 @@ var errNoPassword = errors.New(
 	"account has no password set",
 )
 
-// RegisterUser creates a session with a hashed password
-// and returns session ID, client ID, and token.
-func (database *Database) RegisterUser(
+// SetPassword sets a bcrypt-hashed password on a session,
+// enabling multi-client login via POST /api/v1/login.
+func (database *Database) SetPassword(
 	ctx context.Context,
-	nick, password string,
-) (int64, int64, string, error) {
+	sessionID int64,
+	password string,
+) error {
 	hash, err := bcrypt.GenerateFromPassword(
 		[]byte(password), bcryptCost,
 	)
 	if err != nil {
-		return 0, 0, "", fmt.Errorf(
-			"hash password: %w", err,
-		)
+		return fmt.Errorf("hash password: %w", err)
 	}
 
-	sessionUUID := uuid.New().String()
-	clientUUID := uuid.New().String()
-
-	token, err := generateToken()
+	_, err = database.conn.ExecContext(ctx,
+		"UPDATE sessions SET password_hash = ? WHERE id = ?",
+		string(hash), sessionID)
 	if err != nil {
-		return 0, 0, "", err
+		return fmt.Errorf("set password: %w", err)
 	}
 
-	now := time.Now()
-
-	transaction, err := database.conn.BeginTx(ctx, nil)
-	if err != nil {
-		return 0, 0, "", fmt.Errorf(
-			"begin tx: %w", err,
-		)
-	}
-
-	res, err := transaction.ExecContext(ctx,
-		`INSERT INTO sessions
-		 (uuid, nick, password_hash,
-		  created_at, last_seen)
-		 VALUES (?, ?, ?, ?, ?)`,
-		sessionUUID, nick, string(hash), now, now)
-	if err != nil {
-		_ = transaction.Rollback()
-
-		return 0, 0, "", fmt.Errorf(
-			"create session: %w", err,
-		)
-	}
-
-	sessionID, _ := res.LastInsertId()
-
-	tokenHash := hashToken(token)
-
-	clientRes, err := transaction.ExecContext(ctx,
-		`INSERT INTO clients
-		 (uuid, session_id, token,
-		  created_at, last_seen)
-		 VALUES (?, ?, ?, ?, ?)`,
-		clientUUID, sessionID, tokenHash, now, now)
-	if err != nil {
-		_ = transaction.Rollback()
-
-		return 0, 0, "", fmt.Errorf(
-			"create client: %w", err,
-		)
-	}
-
-	clientID, _ := clientRes.LastInsertId()
-
-	err = transaction.Commit()
-	if err != nil {
-		return 0, 0, "", fmt.Errorf(
-			"commit registration: %w", err,
-		)
-	}
-
-	return sessionID, clientID, token, nil
+	return nil
 }
 
 // LoginUser verifies a nick/password and creates a new

internal/db/auth_test.go

@@ -6,63 +6,65 @@ import (
 	_ "modernc.org/sqlite"
 )
 
-func TestRegisterUser(t *testing.T) {
+func TestSetPassword(t *testing.T) {
 	t.Parallel()
 
 	database := setupTestDB(t)
 	ctx := t.Context()
 
-	sessionID, clientID, token, err :=
-		database.RegisterUser(ctx, "reguser", "password123")
+	sessionID, _, _, err :=
+		database.CreateSession(ctx, "passuser")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if sessionID == 0 || clientID == 0 || token == "" {
+	err = database.SetPassword(
+		ctx, sessionID, "password123",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Verify we can now log in with the password.
+	loginSID, loginCID, loginToken, err :=
+		database.LoginUser(ctx, "passuser", "password123")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if loginSID == 0 || loginCID == 0 || loginToken == "" {
 		t.Fatal("expected valid ids and token")
 	}
-
-	// Verify session works via token lookup.
-	sid, cid, nick, err :=
-		database.GetSessionByToken(ctx, token)
-	if err != nil {
-		t.Fatal(err)
 }
 
-	if sid != sessionID || cid != clientID {
-		t.Fatal("session/client id mismatch")
-	}
-
-	if nick != "reguser" {
-		t.Fatalf("expected reguser, got %s", nick)
-	}
-}
-
-func TestRegisterUserDuplicateNick(t *testing.T) {
+func TestSetPasswordThenWrongLogin(t *testing.T) {
 	t.Parallel()
 
 	database := setupTestDB(t)
 	ctx := t.Context()
 
-	regSID, regCID, regToken, err :=
-		database.RegisterUser(ctx, "dupnick", "password123")
+	sessionID, _, _, err :=
+		database.CreateSession(ctx, "wrongpw")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	_ = regSID
-	_ = regCID
-	_ = regToken
-
-	dupSID, dupCID, dupToken, dupErr :=
-		database.RegisterUser(ctx, "dupnick", "other12345")
-	if dupErr == nil {
-		t.Fatal("expected error for duplicate nick")
+	err = database.SetPassword(
+		ctx, sessionID, "correctpass",
+	)
+	if err != nil {
+		t.Fatal(err)
 	}
 
-	_ = dupSID
-	_ = dupCID
-	_ = dupToken
+	loginSID, loginCID, loginToken, loginErr :=
+		database.LoginUser(ctx, "wrongpw", "wrongpass12")
+	if loginErr == nil {
+		t.Fatal("expected error for wrong password")
+	}
+
+	_ = loginSID
+	_ = loginCID
+	_ = loginToken
 }
 
 func TestLoginUser(t *testing.T) {
@@ -71,23 +73,26 @@ func TestLoginUser(t *testing.T) {
 	database := setupTestDB(t)
 	ctx := t.Context()
 
-	regSID, regCID, regToken, err :=
-		database.RegisterUser(ctx, "loginuser", "mypassword")
+	sessionID, _, _, err :=
+		database.CreateSession(ctx, "loginuser")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	_ = regSID
-	_ = regCID
-	_ = regToken
+	err = database.SetPassword(
+		ctx, sessionID, "mypassword",
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
 
-	sessionID, clientID, token, err :=
+	loginSID, loginCID, token, err :=
 		database.LoginUser(ctx, "loginuser", "mypassword")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	if sessionID == 0 || clientID == 0 || token == "" {
+	if loginSID == 0 || loginCID == 0 || token == "" {
 		t.Fatal("expected valid ids and token")
 	}
 
@@ -103,33 +108,6 @@ func TestLoginUser(t *testing.T) {
 	}
 }
 
-func TestLoginUserWrongPassword(t *testing.T) {
-	t.Parallel()
-
-	database := setupTestDB(t)
-	ctx := t.Context()
-
-	regSID, regCID, regToken, err :=
-		database.RegisterUser(ctx, "wrongpw", "correctpass")
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	_ = regSID
-	_ = regCID
-	_ = regToken
-
-	loginSID, loginCID, loginToken, loginErr :=
-		database.LoginUser(ctx, "wrongpw", "wrongpass12")
-	if loginErr == nil {
-		t.Fatal("expected error for wrong password")
-	}
-
-	_ = loginSID
-	_ = loginCID
-	_ = loginToken
-}
-
 func TestLoginUserNoPassword(t *testing.T) {
 	t.Parallel()
 

internal/db/queries.go

@@ -1305,3 +1305,110 @@ func (database *Database) GetQueueEntryCount(
 
 	return count, nil
 }
+
+// GetChannelHashcashBits returns the hashcash difficulty
+// requirement for a channel. Returns 0 if not set.
+func (database *Database) GetChannelHashcashBits(
+	ctx context.Context,
+	channelID int64,
+) (int, error) {
+	var bits int
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		"SELECT hashcash_bits FROM channels WHERE id = ?",
+		channelID,
+	).Scan(&bits)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"get channel hashcash bits: %w", err,
+		)
+	}
+
+	return bits, nil
+}
+
+// SetChannelHashcashBits sets the hashcash difficulty
+// requirement for a channel. A value of 0 disables the
+// requirement.
+func (database *Database) SetChannelHashcashBits(
+	ctx context.Context,
+	channelID int64,
+	bits int,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`UPDATE channels
+		 SET hashcash_bits = ?, updated_at = ?
+		 WHERE id = ?`,
+		bits, time.Now(), channelID)
+	if err != nil {
+		return fmt.Errorf(
+			"set channel hashcash bits: %w", err,
+		)
+	}
+
+	return nil
+}
+
+// RecordSpentHashcash stores a spent hashcash stamp hash
+// for replay prevention.
+func (database *Database) RecordSpentHashcash(
+	ctx context.Context,
+	stampHash string,
+) error {
+	_, err := database.conn.ExecContext(ctx,
+		`INSERT OR IGNORE INTO spent_hashcash
+		 (stamp_hash, created_at)
+		 VALUES (?, ?)`,
+		stampHash, time.Now())
+	if err != nil {
+		return fmt.Errorf(
+			"record spent hashcash: %w", err,
+		)
+	}
+
+	return nil
+}
+
+// IsHashcashSpent checks whether a hashcash stamp hash
+// has already been used.
+func (database *Database) IsHashcashSpent(
+	ctx context.Context,
+	stampHash string,
+) (bool, error) {
+	var count int
+
+	err := database.conn.QueryRowContext(ctx,
+		`SELECT COUNT(*) FROM spent_hashcash
+		 WHERE stamp_hash = ?`,
+		stampHash,
+	).Scan(&count)
+	if err != nil {
+		return false, fmt.Errorf(
+			"check spent hashcash: %w", err,
+		)
+	}
+
+	return count > 0, nil
+}
+
+// PruneSpentHashcash deletes spent hashcash tokens older
+// than the cutoff and returns the number of rows removed.
+func (database *Database) PruneSpentHashcash(
+	ctx context.Context,
+	cutoff time.Time,
+) (int64, error) {
+	res, err := database.conn.ExecContext(ctx,
+		"DELETE FROM spent_hashcash WHERE created_at < ?",
+		cutoff,
+	)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"prune spent hashcash: %w", err,
+		)
+	}
+
+	deleted, _ := res.RowsAffected()
+
+	return deleted, nil
+}

internal/db/schema/001_initial.sql

@@ -33,6 +33,7 @@ CREATE TABLE IF NOT EXISTS channels (
     topic TEXT NOT NULL DEFAULT '',
     topic_set_by TEXT NOT NULL DEFAULT '',
     topic_set_at DATETIME,
+    hashcash_bits INTEGER NOT NULL DEFAULT 0,
     created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
     updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
@@ -61,6 +62,14 @@ CREATE TABLE IF NOT EXISTS messages (
 CREATE INDEX IF NOT EXISTS idx_messages_to_id ON messages(msg_to, id);
 CREATE INDEX IF NOT EXISTS idx_messages_created ON messages(created_at);
 
+-- Spent hashcash tokens for replay prevention (1-year TTL)
+CREATE TABLE IF NOT EXISTS spent_hashcash (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    stamp_hash TEXT NOT NULL UNIQUE,
+    created_at DATETIME DEFAULT CURRENT_TIMESTAMP
+);
+CREATE INDEX IF NOT EXISTS idx_spent_hashcash_created ON spent_hashcash(created_at);
+
 -- Per-client message queues for fan-out delivery
 CREATE TABLE IF NOT EXISTS client_queues (
     id INTEGER PRIMARY KEY AUTOINCREMENT,

internal/handlers/api.go

@@ -3,6 +3,7 @@ package handlers
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"regexp"
@@ -11,10 +12,16 @@ import (
 	"time"
 
 	"git.eeqj.de/sneak/neoirc/internal/db"
+	"git.eeqj.de/sneak/neoirc/internal/hashcash"
 	"git.eeqj.de/sneak/neoirc/pkg/irc"
 	"github.com/go-chi/chi/v5"
 )
 
+var (
+	errHashcashRequired = errors.New("hashcash required")
+	errHashcashReused   = errors.New("hashcash reused")
+)
+
 var validNickRe = regexp.MustCompile(
 	`^[a-zA-Z_][a-zA-Z0-9_\-\[\]\\^{}|` + "`" + `]{0,31}$`,
 )
@@ -29,6 +36,7 @@ const (
 	defaultMaxBodySize = 4096
 	defaultHistLimit   = 50
 	maxHistLimit       = 500
+	authCookieName     = "neoirc_auth"
 )
 
 func (hdlr *Handlers) maxBodySize() int64 {
@@ -39,23 +47,18 @@ func (hdlr *Handlers) maxBodySize() int64 {
 	return defaultMaxBodySize
 }
 
-// authSession extracts the session from the client token.
+// authSession extracts the session from the auth cookie.
 func (hdlr *Handlers) authSession(
 	request *http.Request,
 ) (int64, int64, string, error) {
-	auth := request.Header.Get("Authorization")
-	if !strings.HasPrefix(auth, "Bearer ") {
-		return 0, 0, "", errUnauthorized
-	}
-
-	token := strings.TrimPrefix(auth, "Bearer ")
-	if token == "" {
+	cookie, err := request.Cookie(authCookieName)
+	if err != nil || cookie.Value == "" {
 		return 0, 0, "", errUnauthorized
 	}
 
 	sessionID, clientID, nick, err :=
 		hdlr.params.Database.GetSessionByToken(
-			request.Context(), token,
+			request.Context(), cookie.Value,
 		)
 	if err != nil {
 		return 0, 0, "", fmt.Errorf("auth: %w", err)
@@ -64,6 +67,46 @@ func (hdlr *Handlers) authSession(
 	return sessionID, clientID, nick, nil
 }
 
+// setAuthCookie sets the authentication cookie on the
+// response.
+func (hdlr *Handlers) setAuthCookie(
+	writer http.ResponseWriter,
+	request *http.Request,
+	token string,
+) {
+	secure := request.TLS != nil ||
+		request.Header.Get("X-Forwarded-Proto") == "https"
+
+	http.SetCookie(writer, &http.Cookie{ //nolint:exhaustruct // optional fields
+		Name:     authCookieName,
+		Value:    token,
+		Path:     "/",
+		HttpOnly: true,
+		Secure:   secure,
+		SameSite: http.SameSiteStrictMode,
+	})
+}
+
+// clearAuthCookie removes the authentication cookie from
+// the client.
+func (hdlr *Handlers) clearAuthCookie(
+	writer http.ResponseWriter,
+	request *http.Request,
+) {
+	secure := request.TLS != nil ||
+		request.Header.Get("X-Forwarded-Proto") == "https"
+
+	http.SetCookie(writer, &http.Cookie{ //nolint:exhaustruct // optional fields
+		Name:     authCookieName,
+		Value:    "",
+		Path:     "/",
+		HttpOnly: true,
+		Secure:   secure,
+		SameSite: http.SameSiteStrictMode,
+		MaxAge:   -1,
+	})
+}
+
 func (hdlr *Handlers) requireAuth(
 	writer http.ResponseWriter,
 	request *http.Request,
@@ -88,10 +131,11 @@ func (hdlr *Handlers) fanOut(
 	request *http.Request,
 	command, from, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 	sessionIDs []int64,
 ) (string, error) {
 	dbID, msgUUID, err := hdlr.params.Database.InsertMessage(
-		request.Context(), command, from, target, nil, body, nil,
+		request.Context(), command, from, target, nil, body, meta,
 	)
 	if err != nil {
 		return "", fmt.Errorf("insert message: %w", err)
@@ -117,10 +161,11 @@ func (hdlr *Handlers) fanOutSilent(
 	request *http.Request,
 	command, from, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 	sessionIDs []int64,
 ) error {
 	_, err := hdlr.fanOut(
-		request, command, from, target, body, sessionIDs,
+		request, command, from, target, body, meta, sessionIDs,
 	)
 
 	return err
@@ -217,10 +262,11 @@ func (hdlr *Handlers) handleCreateSession(
 
 	hdlr.deliverMOTD(request, clientID, sessionID, payload.Nick)
 
+	hdlr.setAuthCookie(writer, request, token)
+
 	hdlr.respondJSON(writer, request, map[string]any{
 		"id":   sessionID,
 		"nick": payload.Nick,
-		"token": token,
 	}, http.StatusCreated)
 }
 
@@ -294,7 +340,7 @@ func (hdlr *Handlers) deliverWelcome(
 		[]string{
 			"CHANTYPES=#",
 			"NICKLEN=32",
-			"CHANMODES=,,," + "imnst",
+			"CHANMODES=,,H," + "imnst",
 			"NETWORK=neoirc",
 			"CASEMAPPING=ascii",
 		},
@@ -825,7 +871,7 @@ func (hdlr *Handlers) HandleSendCommand() http.HandlerFunc {
 			writer, request,
 			sessionID, clientID, nick,
 			payload.Command, payload.To,
-			payload.Body, bodyLines,
+			payload.Body, payload.Meta, bodyLines,
 		)
 	}
 }
@@ -836,6 +882,7 @@ func (hdlr *Handlers) dispatchCommand(
 	sessionID, clientID int64,
 	nick, command, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 	bodyLines func() []string,
 ) {
 	switch command {
@@ -848,7 +895,7 @@ func (hdlr *Handlers) dispatchCommand(
 		hdlr.handlePrivmsg(
 			writer, request,
 			sessionID, clientID, nick,
-			command, target, body, bodyLines,
+			command, target, body, meta, bodyLines,
 		)
 	case irc.CmdJoin:
 		hdlr.handleJoin(
@@ -865,6 +912,11 @@ func (hdlr *Handlers) dispatchCommand(
 			writer, request,
 			sessionID, clientID, nick, bodyLines,
 		)
+	case irc.CmdPass:
+		hdlr.handlePass(
+			writer, request,
+			sessionID, clientID, nick, bodyLines,
+		)
 	case irc.CmdTopic:
 		hdlr.handleTopic(
 			writer, request,
@@ -949,6 +1001,7 @@ func (hdlr *Handlers) handlePrivmsg(
 	sessionID, clientID int64,
 	nick, command, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 	bodyLines func() []string,
 ) {
 	if target == "" {
@@ -986,7 +1039,7 @@ func (hdlr *Handlers) handlePrivmsg(
 		hdlr.handleChannelMsg(
 			writer, request,
 			sessionID, clientID, nick,
-			command, target, body,
+			command, target, body, meta,
 		)
 
 		return
@@ -995,7 +1048,7 @@ func (hdlr *Handlers) handlePrivmsg(
 	hdlr.handleDirectMsg(
 		writer, request,
 		sessionID, clientID, nick,
-		command, target, body,
+		command, target, body, meta,
 	)
 }
 
@@ -1026,6 +1079,7 @@ func (hdlr *Handlers) handleChannelMsg(
 	sessionID, clientID int64,
 	nick, command, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 ) {
 	chID, err := hdlr.params.Database.GetChannelByName(
 		request.Context(), target,
@@ -1066,9 +1120,172 @@ func (hdlr *Handlers) handleChannelMsg(
 		return
 	}
 
-	hdlr.sendChannelMsg(
-		writer, request, command, nick, target, body, chID,
+	hashcashErr := hdlr.validateChannelHashcash(
+		request, clientID, sessionID,
+		writer, nick, target, body, meta, chID,
 	)
+	if hashcashErr != nil {
+		return
+	}
+
+	hdlr.sendChannelMsg(
+		writer, request, command, nick, target,
+		body, meta, chID,
+	)
+}
+
+// validateChannelHashcash checks whether the channel
+// requires hashcash proof-of-work for messages and
+// validates the stamp from the message meta field.
+// Returns nil on success or if the channel has no
+// hashcash requirement. On failure, it sends the
+// appropriate IRC error and returns a non-nil error.
+func (hdlr *Handlers) validateChannelHashcash(
+	request *http.Request,
+	clientID, sessionID int64,
+	writer http.ResponseWriter,
+	nick, target string,
+	body json.RawMessage,
+	meta json.RawMessage,
+	chID int64,
+) error {
+	ctx := request.Context()
+
+	bits, bitsErr := hdlr.params.Database.GetChannelHashcashBits(
+		ctx, chID,
+	)
+	if bitsErr != nil {
+		hdlr.log.Error(
+			"get channel hashcash bits", "error", bitsErr,
+		)
+		hdlr.respondError(
+			writer, request,
+			"internal error",
+			http.StatusInternalServerError,
+		)
+
+		return fmt.Errorf("channel hashcash bits: %w", bitsErr)
+	}
+
+	if bits <= 0 {
+		return nil
+	}
+
+	stamp := hdlr.extractHashcashFromMeta(meta)
+	if stamp == "" {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrCannotSendToChan, nick, []string{target},
+			"Channel requires hashcash proof-of-work",
+		)
+
+		return errHashcashRequired
+	}
+
+	return hdlr.verifyChannelStamp(
+		request, writer,
+		clientID, sessionID,
+		nick, target, body, stamp, bits,
+	)
+}
+
+// verifyChannelStamp validates a channel hashcash stamp
+// and checks for replay attacks.
+func (hdlr *Handlers) verifyChannelStamp(
+	request *http.Request,
+	writer http.ResponseWriter,
+	clientID, sessionID int64,
+	nick, target string,
+	body json.RawMessage,
+	stamp string,
+	bits int,
+) error {
+	ctx := request.Context()
+	bodyHashStr := hashcash.BodyHash(body)
+
+	valErr := hdlr.channelHashcash.ValidateStamp(
+		stamp, bits, target, bodyHashStr,
+	)
+	if valErr != nil {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrCannotSendToChan, nick, []string{target},
+			"Invalid hashcash: "+valErr.Error(),
+		)
+
+		return fmt.Errorf("channel hashcash: %w", valErr)
+	}
+
+	stampKey := hashcash.StampHash(stamp)
+
+	spent, spentErr := hdlr.params.Database.IsHashcashSpent(
+		ctx, stampKey,
+	)
+	if spentErr != nil {
+		hdlr.log.Error(
+			"check spent hashcash", "error", spentErr,
+		)
+		hdlr.respondError(
+			writer, request,
+			"internal error",
+			http.StatusInternalServerError,
+		)
+
+		return fmt.Errorf("check spent hashcash: %w", spentErr)
+	}
+
+	if spent {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrCannotSendToChan, nick, []string{target},
+			"Hashcash stamp already used",
+		)
+
+		return errHashcashReused
+	}
+
+	recordErr := hdlr.params.Database.RecordSpentHashcash(
+		ctx, stampKey,
+	)
+	if recordErr != nil {
+		hdlr.log.Error(
+			"record spent hashcash", "error", recordErr,
+		)
+	}
+
+	return nil
+}
+
+// extractHashcashFromMeta parses the meta JSON and
+// returns the hashcash stamp string, or empty string
+// if not present.
+func (hdlr *Handlers) extractHashcashFromMeta(
+	meta json.RawMessage,
+) string {
+	if len(meta) == 0 {
+		return ""
+	}
+
+	var metaMap map[string]json.RawMessage
+
+	err := json.Unmarshal(meta, &metaMap)
+	if err != nil {
+		return ""
+	}
+
+	raw, ok := metaMap["hashcash"]
+	if !ok {
+		return ""
+	}
+
+	var stamp string
+
+	err = json.Unmarshal(raw, &stamp)
+	if err != nil {
+		return ""
+	}
+
+	return stamp
 }
 
 func (hdlr *Handlers) sendChannelMsg(
@@ -1076,6 +1293,7 @@ func (hdlr *Handlers) sendChannelMsg(
 	request *http.Request,
 	command, nick, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 	chID int64,
 ) {
 	memberIDs, err := hdlr.params.Database.GetChannelMemberIDs(
@@ -1095,7 +1313,7 @@ func (hdlr *Handlers) sendChannelMsg(
 	}
 
 	msgUUID, err := hdlr.fanOut(
-		request, command, nick, target, body, memberIDs,
+		request, command, nick, target, body, meta, memberIDs,
 	)
 	if err != nil {
 		hdlr.log.Error("send message failed", "error", err)
@@ -1119,6 +1337,7 @@ func (hdlr *Handlers) handleDirectMsg(
 	sessionID, clientID int64,
 	nick, command, target string,
 	body json.RawMessage,
+	meta json.RawMessage,
 ) {
 	targetSID, err := hdlr.params.Database.GetSessionByNick(
 		request.Context(), target,
@@ -1143,7 +1362,7 @@ func (hdlr *Handlers) handleDirectMsg(
 	}
 
 	msgUUID, err := hdlr.fanOut(
-		request, command, nick, target, body, recipients,
+		request, command, nick, target, body, meta, recipients,
 	)
 	if err != nil {
 		hdlr.log.Error("send dm failed", "error", err)
@@ -1254,7 +1473,7 @@ func (hdlr *Handlers) executeJoin(
 	)
 
 	_ = hdlr.fanOutSilent(
-		request, irc.CmdJoin, nick, channel, nil, memberIDs,
+		request, irc.CmdJoin, nick, channel, nil, nil, memberIDs,
 	)
 
 	hdlr.deliverJoinNumerics(
@@ -1424,7 +1643,7 @@ func (hdlr *Handlers) handlePart(
 	)
 
 	_ = hdlr.fanOutSilent(
-		request, irc.CmdPart, nick, channel, body, memberIDs,
+		request, irc.CmdPart, nick, channel, body, nil, memberIDs,
 	)
 
 	err = hdlr.params.Database.PartChannel(
@@ -1704,7 +1923,7 @@ func (hdlr *Handlers) executeTopic(
 	)
 
 	_ = hdlr.fanOutSilent(
-		request, irc.CmdTopic, nick, channel, body, memberIDs,
+		request, irc.CmdTopic, nick, channel, body, nil, memberIDs,
 	)
 
 	hdlr.enqueueNumeric(
@@ -1828,6 +2047,8 @@ func (hdlr *Handlers) handleQuit(
 		request.Context(), sessionID,
 	)
 
+	hdlr.clearAuthCookie(writer, request)
+
 	hdlr.respondJSON(writer, request,
 		map[string]string{"status": "quit"},
 		http.StatusOK)
@@ -1867,11 +2088,10 @@ func (hdlr *Handlers) handleMode(
 		return
 	}
 
-	_ = bodyLines
-
 	hdlr.handleChannelMode(
 		writer, request,
 		sessionID, clientID, nick, channel,
+		bodyLines,
 	)
 }
 
@@ -1880,6 +2100,7 @@ func (hdlr *Handlers) handleChannelMode(
 	request *http.Request,
 	sessionID, clientID int64,
 	nick, channel string,
+	bodyLines func() []string,
 ) {
 	ctx := request.Context()
 
@@ -1896,10 +2117,47 @@ func (hdlr *Handlers) handleChannelMode(
 		return
 	}
 
+	lines := bodyLines()
+	if len(lines) > 0 {
+		hdlr.applyChannelMode(
+			writer, request,
+			sessionID, clientID, nick,
+			channel, chID, lines,
+		)
+
+		return
+	}
+
+	hdlr.queryChannelMode(
+		writer, request,
+		sessionID, clientID, nick, channel, chID,
+	)
+}
+
+// queryChannelMode sends RPL_CHANNELMODEIS and
+// RPL_CREATIONTIME for a channel. Includes +H if
+// the channel has a hashcash requirement.
+func (hdlr *Handlers) queryChannelMode(
+	writer http.ResponseWriter,
+	request *http.Request,
+	sessionID, clientID int64,
+	nick, channel string,
+	chID int64,
+) {
+	ctx := request.Context()
+
+	modeStr := "+n"
+
+	bits, bitsErr := hdlr.params.Database.
+		GetChannelHashcashBits(ctx, chID)
+	if bitsErr == nil && bits > 0 {
+		modeStr = fmt.Sprintf("+nH %d", bits)
+	}
+
 	// 324 RPL_CHANNELMODEIS
 	hdlr.enqueueNumeric(
 		ctx, clientID, irc.RplChannelModeIs, nick,
-		[]string{channel, "+n"}, "",
+		[]string{channel, modeStr}, "",
 	)
 
 	// 329 RPL_CREATIONTIME
@@ -1924,6 +2182,156 @@ func (hdlr *Handlers) handleChannelMode(
 		http.StatusOK)
 }
 
+// applyChannelMode handles setting channel modes.
+// Currently supports +H/-H for hashcash bits.
+func (hdlr *Handlers) applyChannelMode(
+	writer http.ResponseWriter,
+	request *http.Request,
+	sessionID, clientID int64,
+	nick, channel string,
+	chID int64,
+	modeArgs []string,
+) {
+	ctx := request.Context()
+	modeStr := modeArgs[0]
+
+	switch modeStr {
+	case "+H":
+		hdlr.setHashcashMode(
+			writer, request,
+			sessionID, clientID, nick,
+			channel, chID, modeArgs,
+		)
+	case "-H":
+		hdlr.clearHashcashMode(
+			writer, request,
+			sessionID, clientID, nick,
+			channel, chID,
+		)
+	default:
+		// Unknown or unsupported mode change.
+		hdlr.enqueueNumeric(
+			ctx, clientID, irc.ErrUnknownMode, nick,
+			[]string{modeStr},
+			"is unknown mode char to me",
+		)
+		hdlr.broker.Notify(sessionID)
+		hdlr.respondJSON(writer, request,
+			map[string]string{"status": "error"},
+			http.StatusOK)
+	}
+}
+
+const (
+	// minHashcashBits is the minimum allowed hashcash
+	// difficulty for channels.
+	minHashcashBits = 1
+	// maxHashcashBits is the maximum allowed hashcash
+	// difficulty for channels.
+	maxHashcashBits = 40
+)
+
+// setHashcashMode handles MODE #channel +H <bits>.
+func (hdlr *Handlers) setHashcashMode(
+	writer http.ResponseWriter,
+	request *http.Request,
+	sessionID, clientID int64,
+	nick, channel string,
+	chID int64,
+	modeArgs []string,
+) {
+	ctx := request.Context()
+
+	if len(modeArgs) < 2 { //nolint:mnd // +H requires a bits arg
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrNeedMoreParams, nick, []string{irc.CmdMode},
+			"Not enough parameters (+H requires bits)",
+		)
+
+		return
+	}
+
+	bits, err := strconv.Atoi(modeArgs[1])
+	if err != nil || bits < minHashcashBits ||
+		bits > maxHashcashBits {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrUnknownMode, nick, []string{"+H"},
+			fmt.Sprintf(
+				"Invalid hashcash bits (must be %d-%d)",
+				minHashcashBits, maxHashcashBits,
+			),
+		)
+
+		return
+	}
+
+	err = hdlr.params.Database.SetChannelHashcashBits(
+		ctx, chID, bits,
+	)
+	if err != nil {
+		hdlr.log.Error(
+			"set channel hashcash bits", "error", err,
+		)
+		hdlr.respondError(
+			writer, request,
+			"internal error",
+			http.StatusInternalServerError,
+		)
+
+		return
+	}
+
+	hdlr.enqueueNumeric(
+		ctx, clientID, irc.RplChannelModeIs, nick,
+		[]string{
+			channel,
+			fmt.Sprintf("+H %d", bits),
+		}, "",
+	)
+	hdlr.broker.Notify(sessionID)
+	hdlr.respondJSON(writer, request,
+		map[string]string{"status": "ok"},
+		http.StatusOK)
+}
+
+// clearHashcashMode handles MODE #channel -H.
+func (hdlr *Handlers) clearHashcashMode(
+	writer http.ResponseWriter,
+	request *http.Request,
+	sessionID, clientID int64,
+	nick, channel string,
+	chID int64,
+) {
+	ctx := request.Context()
+
+	err := hdlr.params.Database.SetChannelHashcashBits(
+		ctx, chID, 0,
+	)
+	if err != nil {
+		hdlr.log.Error(
+			"clear channel hashcash bits", "error", err,
+		)
+		hdlr.respondError(
+			writer, request,
+			"internal error",
+			http.StatusInternalServerError,
+		)
+
+		return
+	}
+
+	hdlr.enqueueNumeric(
+		ctx, clientID, irc.RplChannelModeIs, nick,
+		[]string{channel, "+n"}, "",
+	)
+	hdlr.broker.Notify(sessionID)
+	hdlr.respondJSON(writer, request,
+		map[string]string{"status": "ok"},
+		http.StatusOK)
+}
+
 // handleNames sends NAMES reply for a channel.
 func (hdlr *Handlers) handleNames(
 	writer http.ResponseWriter,
@@ -2443,6 +2851,8 @@ func (hdlr *Handlers) HandleLogout() http.HandlerFunc {
 			)
 		}
 
+		hdlr.clearAuthCookie(writer, request)
+
 		hdlr.respondJSON(writer, request,
 			map[string]string{"status": "ok"},
 			http.StatusOK)

internal/handlers/api_test.go

@@ -22,6 +22,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/globals"
 	"git.eeqj.de/sneak/neoirc/internal/handlers"
+	"git.eeqj.de/sneak/neoirc/internal/hashcash"
 	"git.eeqj.de/sneak/neoirc/internal/healthcheck"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
 	"git.eeqj.de/sneak/neoirc/internal/middleware"
@@ -41,6 +42,7 @@ const (
 	apiMessages    = "/api/v1/messages"
 	apiSession     = "/api/v1/session"
 	apiState       = "/api/v1/state"
+	authCookieName = "neoirc_auth"
 )
 
 // testServer wraps a test HTTP server with helpers.
@@ -260,7 +262,7 @@ func doRequest(
 
 func doRequestAuth(
 	t *testing.T,
-	method, url, token string,
+	method, url, cookie string,
 	body io.Reader,
 ) (*http.Response, error) {
 	t.Helper()
@@ -278,10 +280,11 @@ func doRequestAuth(
 		)
 	}
 
-	if token != "" {
-		request.Header.Set(
-			"Authorization", "Bearer "+token,
-		)
+	if cookie != "" {
+		request.AddCookie(&http.Cookie{ //nolint:exhaustruct // only name+value needed
+			Name:  authCookieName,
+			Value: cookie,
+		})
 	}
 
 	resp, err := http.DefaultClient.Do(request)
@@ -324,17 +327,19 @@ func (tserver *testServer) createSession(
 		)
 	}
 
-	var result struct {
-		ID    int64  `json:"id"`
-		Token string `json:"token"`
+	// Drain the body.
+	_, _ = io.ReadAll(resp.Body)
+
+	// Extract auth cookie from response.
+	for _, cookie := range resp.Cookies() {
+		if cookie.Name == authCookieName {
+			return cookie.Value
+		}
 	}
 
-	decErr := json.NewDecoder(resp.Body).Decode(&result)
-	if decErr != nil {
-		tserver.t.Fatalf("decode session: %v", decErr)
-	}
+	tserver.t.Fatal("no auth cookie in response")
 
-	return result.Token
+	return ""
 }
 
 func (tserver *testServer) sendCommand(
@@ -491,10 +496,10 @@ func findNumeric(
 
 func TestCreateSessionValid(t *testing.T) {
 	tserver := newTestServer(t)
-	token := tserver.createSession("alice")
+	cookie := tserver.createSession("alice")
 
-	if token == "" {
-		t.Fatal("expected token")
+	if cookie == "" {
+		t.Fatal("expected auth cookie")
 	}
 }
 
@@ -616,7 +621,7 @@ func TestCreateSessionMalformed(t *testing.T) {
 	}
 }
 
-func TestAuthNoHeader(t *testing.T) {
+func TestAuthNoCookie(t *testing.T) {
 	tserver := newTestServer(t)
 
 	status, _ := tserver.getState("")
@@ -625,11 +630,11 @@ func TestAuthNoHeader(t *testing.T) {
 	}
 }
 
-func TestAuthBadToken(t *testing.T) {
+func TestAuthBadCookie(t *testing.T) {
 	tserver := newTestServer(t)
 
 	status, _ := tserver.getState(
-		"invalid-token-12345",
+		"invalid-cookie-12345",
 	)
 	if status != http.StatusUnauthorized {
 		t.Fatalf("expected 401, got %d", status)
@@ -1826,90 +1831,6 @@ func assertFieldGTE(
 	}
 }
 
-func TestRegisterValid(t *testing.T) {
-	tserver := newTestServer(t)
-
-	body, err := json.Marshal(map[string]string{
-		"nick": "reguser", "password": "password123",
-	})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	resp, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/register"),
-		bytes.NewReader(body),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	defer func() { _ = resp.Body.Close() }()
-
-	if resp.StatusCode != http.StatusCreated {
-		respBody, _ := io.ReadAll(resp.Body)
-		t.Fatalf(
-			"expected 201, got %d: %s",
-			resp.StatusCode, respBody,
-		)
-	}
-
-	var result map[string]any
-
-	_ = json.NewDecoder(resp.Body).Decode(&result)
-
-	if result["token"] == nil || result["token"] == "" {
-		t.Fatal("expected token in response")
-	}
-
-	if result["nick"] != "reguser" {
-		t.Fatalf(
-			"expected reguser, got %v", result["nick"],
-		)
-	}
-}
-
-func TestRegisterDuplicate(t *testing.T) {
-	tserver := newTestServer(t)
-
-	body, err := json.Marshal(map[string]string{
-		"nick": "dupuser", "password": "password123",
-	})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	resp, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/register"),
-		bytes.NewReader(body),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	_ = resp.Body.Close()
-
-	resp2, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/register"),
-		bytes.NewReader(body),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	defer func() { _ = resp2.Body.Close() }()
-
-	if resp2.StatusCode != http.StatusConflict {
-		t.Fatalf("expected 409, got %d", resp2.StatusCode)
-	}
-}
-
 func postJSONExpectStatus(
 	t *testing.T,
 	tserver *testServer,
@@ -1944,36 +1865,102 @@ func postJSONExpectStatus(
 	}
 }
 
-func TestRegisterShortPassword(t *testing.T) {
+func TestPassCommand(t *testing.T) {
 	tserver := newTestServer(t)
+	token := tserver.createSession("passuser")
 
-	postJSONExpectStatus(
-		t, tserver, "/api/v1/register",
-		map[string]string{
-			"nick": "shortpw", "password": "short",
+	// Drain initial messages.
+	_, _ = tserver.pollMessages(token, 0)
+
+	// Set password via PASS command.
+	status, result := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: "PASS",
+			bodyKey:    []string{"s3cure_pass"},
 		},
-		http.StatusBadRequest,
+	)
+	if status != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d: %v", status, result,
 		)
 	}
 
-func TestRegisterInvalidNick(t *testing.T) {
-	tserver := newTestServer(t)
-
-	postJSONExpectStatus(
-		t, tserver, "/api/v1/register",
-		map[string]string{
-			"nick":     "bad nick!",
-			"password": "password123",
-		},
-		http.StatusBadRequest,
+	if result[statusKey] != "ok" {
+		t.Fatalf(
+			"expected ok, got %v", result[statusKey],
 		)
 	}
+}
+
+func TestPassCommandShortPassword(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("shortpw")
+
+	// Drain initial messages.
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Try short password — should fail.
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: "PASS",
+			bodyKey:    []string{"short"},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	if !findNumeric(msgs, "461") {
+		t.Fatalf(
+			"expected ERR_NEEDMOREPARAMS (461), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestPassCommandEmpty(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("emptypw")
+
+	// Drain initial messages.
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Try empty password — should fail.
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{commandKey: "PASS"},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	if !findNumeric(msgs, "461") {
+		t.Fatalf(
+			"expected ERR_NEEDMOREPARAMS (461), got %v",
+			msgs,
+		)
+	}
+}
 
 func TestLoginValid(t *testing.T) {
 	tserver := newTestServer(t)
 
-	// Register first.
-	regBody, err := json.Marshal(map[string]string{
+	// Create session and set password via PASS command.
+	token := tserver.createSession("loginuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: "PASS",
+		bodyKey:    []string{"password123"},
+	})
+
+	// Login with nick + password.
+	loginBody, err := json.Marshal(map[string]string{
 		"nick": "loginuser", "password": "password123",
 	})
 	if err != nil {
@@ -1981,26 +1968,6 @@ func TestLoginValid(t *testing.T) {
 	}
 
 	resp, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/register"),
-		bytes.NewReader(regBody),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	_ = resp.Body.Close()
-
-	// Login.
-	loginBody, err := json.Marshal(map[string]string{
-		"nick": "loginuser", "password": "password123",
-	})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	resp2, err := doRequest(
 		t,
 		http.MethodPost,
 		tserver.url("/api/v1/login"),
@@ -2010,31 +1977,33 @@ func TestLoginValid(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	defer func() { _ = resp2.Body.Close() }()
+	defer func() { _ = resp.Body.Close() }()
 
-	if resp2.StatusCode != http.StatusOK {
-		respBody, _ := io.ReadAll(resp2.Body)
+	if resp.StatusCode != http.StatusOK {
+		respBody, _ := io.ReadAll(resp.Body)
 		t.Fatalf(
 			"expected 200, got %d: %s",
-			resp2.StatusCode, respBody,
+			resp.StatusCode, respBody,
 		)
 	}
 
-	var result map[string]any
+	// Extract auth cookie from login response.
+	var loginCookie string
 
-	_ = json.NewDecoder(resp2.Body).Decode(&result)
+	for _, cookie := range resp.Cookies() {
+		if cookie.Name == authCookieName {
+			loginCookie = cookie.Value
 
-	if result["token"] == nil || result["token"] == "" {
-		t.Fatal("expected token in response")
+			break
+		}
 	}
 
-	// Verify token works.
-	token, ok := result["token"].(string)
-	if !ok {
-		t.Fatal("token not a string")
+	if loginCookie == "" {
+		t.Fatal("expected auth cookie from login")
 	}
 
-	status, state := tserver.getState(token)
+	// Verify login cookie works for auth.
+	status, state := tserver.getState(loginCookie)
 	if status != http.StatusOK {
 		t.Fatalf("expected 200, got %d", status)
 	}
@@ -2050,49 +2019,22 @@ func TestLoginValid(t *testing.T) {
 func TestLoginWrongPassword(t *testing.T) {
 	tserver := newTestServer(t)
 
-	regBody, err := json.Marshal(map[string]string{
-		"nick": "wrongpwuser", "password": "correctpass1",
+	// Create session and set password via PASS command.
+	token := tserver.createSession("wrongpwuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: "PASS",
+		bodyKey:    []string{"correctpass1"},
 	})
-	if err != nil {
-		t.Fatal(err)
-	}
 
-	resp, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/register"),
-		bytes.NewReader(regBody),
+	postJSONExpectStatus(
+		t, tserver, "/api/v1/login",
+		map[string]string{
+			"nick":     "wrongpwuser",
+			"password": "wrongpass12",
+		},
+		http.StatusUnauthorized,
 	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	_ = resp.Body.Close()
-
-	loginBody, err := json.Marshal(map[string]string{
-		"nick": "wrongpwuser", "password": "wrongpass12",
-	})
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	resp2, err := doRequest(
-		t,
-		http.MethodPost,
-		tserver.url("/api/v1/login"),
-		bytes.NewReader(loginBody),
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	defer func() { _ = resp2.Body.Close() }()
-
-	if resp2.StatusCode != http.StatusUnauthorized {
-		t.Fatalf(
-			"expected 401, got %d", resp2.StatusCode,
-		)
-	}
 }
 
 func TestLoginNonexistentUser(t *testing.T) {
@@ -2108,13 +2050,74 @@ func TestLoginNonexistentUser(t *testing.T) {
 	)
 }
 
+func TestSessionCookie(t *testing.T) {
+	tserver := newTestServer(t)
+
+	body, err := json.Marshal(
+		map[string]string{"nick": "cookietest"},
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	resp, err := doRequest(
+		t,
+		http.MethodPost,
+		tserver.url(apiSession),
+		bytes.NewReader(body),
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusCreated {
+		t.Fatalf(
+			"expected 201, got %d", resp.StatusCode,
+		)
+	}
+
+	// Verify Set-Cookie header.
+	var authCookie *http.Cookie
+
+	for _, cookie := range resp.Cookies() {
+		if cookie.Name == authCookieName {
+			authCookie = cookie
+
+			break
+		}
+	}
+
+	if authCookie == nil {
+		t.Fatal("expected neoirc_auth cookie")
+	}
+
+	if !authCookie.HttpOnly {
+		t.Fatal("cookie should be HttpOnly")
+	}
+
+	if authCookie.SameSite != http.SameSiteStrictMode {
+		t.Fatal("cookie should be SameSite=Strict")
+	}
+
+	// Verify JSON body does NOT contain token.
+	var result map[string]any
+
+	_ = json.NewDecoder(resp.Body).Decode(&result)
+
+	if _, hasToken := result["token"]; hasToken {
+		t.Fatal("JSON body should not contain token")
+	}
+}
+
 func TestSessionStillWorks(t *testing.T) {
 	tserver := newTestServer(t)
 
 	// Verify anonymous session creation still works.
 	token := tserver.createSession("anon_user")
 	if token == "" {
-		t.Fatal("expected token for anonymous session")
+		t.Fatal("expected cookie for anonymous session")
 	}
 
 	status, state := tserver.getState(token)
@@ -2157,3 +2160,397 @@ func TestNickBroadcastToChannels(t *testing.T) {
 		)
 	}
 }
+
+// --- Channel Hashcash Tests ---
+
+const (
+	metaKey     = "meta"
+	modeCmd     = "MODE"
+	hashcashKey = "hashcash"
+)
+
+func mintTestChannelHashcash(
+	tb testing.TB,
+	bits int,
+	channel string,
+	body json.RawMessage,
+) string {
+	tb.Helper()
+
+	bodyHash := hashcash.BodyHash(body)
+
+	return hashcash.MintChannelStamp(bits, channel, bodyHash)
+}
+
+func TestChannelHashcashSetMode(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcmode_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hctest",
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Set hashcash bits to 2 via MODE +H.
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: modeCmd,
+			toKey:      "#hctest",
+			bodyKey:    []string{"+H", "2"},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	// Should get RPL_CHANNELMODEIS (324) confirming +H.
+	if !findNumeric(msgs, "324") {
+		t.Fatalf(
+			"expected RPL_CHANNELMODEIS (324), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestChannelHashcashQueryMode(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcquery_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcquery",
+	})
+
+	// Set hashcash bits.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcquery",
+		bodyKey:    []string{"+H", "5"},
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Query mode — should show +nH.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcquery",
+	})
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	found := false
+
+	for _, msg := range msgs {
+		code, ok := msg["code"].(float64)
+		if ok && int(code) == 324 {
+			found = true
+		}
+	}
+
+	if !found {
+		t.Fatalf(
+			"expected RPL_CHANNELMODEIS (324), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestChannelHashcashClearMode(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcclear_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcclear",
+	})
+
+	// Set hashcash bits.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcclear",
+		bodyKey:    []string{"+H", "5"},
+	})
+
+	// Clear hashcash bits.
+	status, _ := tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcclear",
+		bodyKey:    []string{"-H"},
+	})
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	// Now message should succeed without hashcash.
+	status, result := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#hcclear",
+			bodyKey:    []string{"test message"},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d: %v", status, result,
+		)
+	}
+}
+
+func TestChannelHashcashRejectNoStamp(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcreject_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcreject",
+	})
+
+	// Set hashcash requirement.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcreject",
+		bodyKey:    []string{"+H", "2"},
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Send message without hashcash — should fail.
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#hcreject",
+			bodyKey:    []string{"spam message"},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	// Should get ERR_CANNOTSENDTOCHAN (404).
+	if !findNumeric(msgs, "404") {
+		t.Fatalf(
+			"expected ERR_CANNOTSENDTOCHAN (404), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestChannelHashcashAcceptValidStamp(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcaccept_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcaccept",
+	})
+
+	// Set hashcash requirement (2 bits = fast to mint).
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcaccept",
+		bodyKey:    []string{"+H", "2"},
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Mint a valid hashcash stamp.
+	msgBody, marshalErr := json.Marshal(
+		[]string{"hello world"},
+	)
+	if marshalErr != nil {
+		t.Fatal(marshalErr)
+	}
+
+	stamp := mintTestChannelHashcash(
+		t, 2, "#hcaccept", msgBody,
+	)
+
+	// Send message with valid hashcash.
+	status, result := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#hcaccept",
+			bodyKey:    []string{"hello world"},
+			metaKey: map[string]any{
+				hashcashKey: stamp,
+			},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d: %v", status, result,
+		)
+	}
+
+	if result["id"] == nil || result["id"] == "" {
+		t.Fatal("expected message id for valid hashcash")
+	}
+
+	// Verify the message was delivered.
+	msgs, _ := tserver.pollMessages(token, lastID)
+	if !findMessage(msgs, privmsgCmd, "hcaccept_user") {
+		t.Fatalf(
+			"message not received: %v", msgs,
+		)
+	}
+}
+
+func TestChannelHashcashRejectReplayedStamp(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcreplay_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcreplay",
+	})
+
+	// Set hashcash requirement.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcreplay",
+		bodyKey:    []string{"+H", "2"},
+	})
+
+	_, _ = tserver.pollMessages(token, 0)
+
+	// Mint and send once — should succeed.
+	msgBody, marshalErr := json.Marshal(
+		[]string{"unique msg"},
+	)
+	if marshalErr != nil {
+		t.Fatal(marshalErr)
+	}
+
+	stamp := mintTestChannelHashcash(
+		t, 2, "#hcreplay", msgBody,
+	)
+
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#hcreplay",
+			bodyKey:    []string{"unique msg"},
+			metaKey: map[string]any{
+				hashcashKey: stamp,
+			},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Replay the same stamp — should fail.
+	status, _ = tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#hcreplay",
+			bodyKey:    []string{"unique msg"},
+			metaKey: map[string]any{
+				hashcashKey: stamp,
+			},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf("expected 200, got %d", status)
+	}
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	// Should get ERR_CANNOTSENDTOCHAN (404).
+	if !findNumeric(msgs, "404") {
+		t.Fatalf(
+			"expected replay rejection (404), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestChannelHashcashNoRequirementWorks(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcnone_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#nohashcash",
+	})
+
+	// No hashcash set — message should work.
+	status, result := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: privmsgCmd,
+			toKey:      "#nohashcash",
+			bodyKey:    []string{"free message"},
+		},
+	)
+	if status != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d: %v", status, result,
+		)
+	}
+
+	if result["id"] == nil || result["id"] == "" {
+		t.Fatal("expected message id")
+	}
+}
+
+func TestChannelHashcashInvalidBitsRange(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcbits_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcbits",
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Try to set bits to 0 — should fail.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcbits",
+		bodyKey:    []string{"+H", "0"},
+	})
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	if !findNumeric(msgs, "472") {
+		t.Fatalf(
+			"expected ERR_UNKNOWNMODE (472), got %v",
+			msgs,
+		)
+	}
+}
+
+func TestChannelHashcashMissingBitsArg(t *testing.T) {
+	tserver := newTestServer(t)
+	token := tserver.createSession("hcnoarg_user")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#hcnoarg",
+	})
+
+	_, lastID := tserver.pollMessages(token, 0)
+
+	// Try to set +H without bits argument.
+	tserver.sendCommand(token, map[string]any{
+		commandKey: modeCmd,
+		toKey:      "#hcnoarg",
+		bodyKey:    []string{"+H"},
+	})
+
+	msgs, _ := tserver.pollMessages(token, lastID)
+
+	if !findNumeric(msgs, "461") {
+		t.Fatalf(
+			"expected ERR_NEEDMOREPARAMS (461), got %v",
+			msgs,
+		)
+	}
+}

internal/handlers/auth.go

@@ -5,120 +5,11 @@ import (
 	"net/http"
 	"strings"
 
-	"git.eeqj.de/sneak/neoirc/internal/db"
+	"git.eeqj.de/sneak/neoirc/pkg/irc"
 )
 
 const minPasswordLength = 8
 
-// HandleRegister creates a new user with a password.
-func (hdlr *Handlers) HandleRegister() http.HandlerFunc {
-	return func(
-		writer http.ResponseWriter,
-		request *http.Request,
-	) {
-		request.Body = http.MaxBytesReader(
-			writer, request.Body, hdlr.maxBodySize(),
-		)
-
-		hdlr.handleRegister(writer, request)
-	}
-}
-
-func (hdlr *Handlers) handleRegister(
-	writer http.ResponseWriter,
-	request *http.Request,
-) {
-	type registerRequest struct {
-		Nick     string `json:"nick"`
-		Password string `json:"password"`
-	}
-
-	var payload registerRequest
-
-	err := json.NewDecoder(request.Body).Decode(&payload)
-	if err != nil {
-		hdlr.respondError(
-			writer, request,
-			"invalid request body",
-			http.StatusBadRequest,
-		)
-
-		return
-	}
-
-	payload.Nick = strings.TrimSpace(payload.Nick)
-
-	if !validNickRe.MatchString(payload.Nick) {
-		hdlr.respondError(
-			writer, request,
-			"invalid nick format",
-			http.StatusBadRequest,
-		)
-
-		return
-	}
-
-	if len(payload.Password) < minPasswordLength {
-		hdlr.respondError(
-			writer, request,
-			"password must be at least 8 characters",
-			http.StatusBadRequest,
-		)
-
-		return
-	}
-
-	sessionID, clientID, token, err :=
-		hdlr.params.Database.RegisterUser(
-			request.Context(),
-			payload.Nick,
-			payload.Password,
-		)
-	if err != nil {
-		hdlr.handleRegisterError(
-			writer, request, err,
-		)
-
-		return
-	}
-
-	hdlr.stats.IncrSessions()
-	hdlr.stats.IncrConnections()
-
-	hdlr.deliverMOTD(request, clientID, sessionID, payload.Nick)
-
-	hdlr.respondJSON(writer, request, map[string]any{
-		"id":    sessionID,
-		"nick":  payload.Nick,
-		"token": token,
-	}, http.StatusCreated)
-}
-
-func (hdlr *Handlers) handleRegisterError(
-	writer http.ResponseWriter,
-	request *http.Request,
-	err error,
-) {
-	if db.IsUniqueConstraintError(err) {
-		hdlr.respondError(
-			writer, request,
-			"nick already taken",
-			http.StatusConflict,
-		)
-
-		return
-	}
-
-	hdlr.log.Error(
-		"register user failed", "error", err,
-	)
-	hdlr.respondError(
-		writer, request,
-		"internal error",
-		http.StatusInternalServerError,
-	)
-}
-
 // HandleLogin authenticates a user with nick and password.
 func (hdlr *Handlers) HandleLogin() http.HandlerFunc {
 	return func(
@@ -195,9 +86,66 @@ func (hdlr *Handlers) handleLogin(
 		request, clientID, sessionID, payload.Nick,
 	)
 
+	hdlr.setAuthCookie(writer, request, token)
+
 	hdlr.respondJSON(writer, request, map[string]any{
 		"id":   sessionID,
 		"nick": payload.Nick,
-		"token": token,
 	}, http.StatusOK)
 }
+
+// handlePass handles the IRC PASS command to set a
+// password on the authenticated session, enabling
+// multi-client login via POST /api/v1/login.
+func (hdlr *Handlers) handlePass(
+	writer http.ResponseWriter,
+	request *http.Request,
+	sessionID, clientID int64,
+	nick string,
+	bodyLines func() []string,
+) {
+	lines := bodyLines()
+	if len(lines) == 0 || lines[0] == "" {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrNeedMoreParams, nick,
+			[]string{irc.CmdPass},
+			"Not enough parameters",
+		)
+
+		return
+	}
+
+	password := lines[0]
+
+	if len(password) < minPasswordLength {
+		hdlr.respondIRCError(
+			writer, request, clientID, sessionID,
+			irc.ErrNeedMoreParams, nick,
+			[]string{irc.CmdPass},
+			"Password must be at least 8 characters",
+		)
+
+		return
+	}
+
+	err := hdlr.params.Database.SetPassword(
+		request.Context(), sessionID, password,
+	)
+	if err != nil {
+		hdlr.log.Error(
+			"set password failed", "error", err,
+		)
+		hdlr.respondError(
+			writer, request,
+			"internal error",
+			http.StatusInternalServerError,
+		)
+
+		return
+	}
+
+	hdlr.respondJSON(writer, request,
+		map[string]string{"status": "ok"},
+		http.StatusOK)
+}

internal/handlers/handlers.go

@@ -36,6 +36,11 @@ type Params struct {
 
 const defaultIdleTimeout = 30 * 24 * time.Hour
 
+// spentHashcashTTL is how long spent hashcash tokens are
+// retained for replay prevention. Per issue requirements,
+// this is 1 year.
+const spentHashcashTTL = 365 * 24 * time.Hour
+
 // Handlers manages HTTP request handling.
 type Handlers struct {
 	params          *Params
@@ -43,6 +48,7 @@ type Handlers struct {
 	hc              *healthcheck.Healthcheck
 	broker          *broker.Broker
 	hashcashVal     *hashcash.Validator
+	channelHashcash *hashcash.ChannelValidator
 	stats           *stats.Tracker
 	cancelCleanup   context.CancelFunc
 }
@@ -63,6 +69,7 @@ func New(
 		hc:              params.Healthcheck,
 		broker:          broker.New(),
 		hashcashVal:     hashcash.NewValidator(resource),
+		channelHashcash: hashcash.NewChannelValidator(),
 		stats:           params.Stats,
 	}
 
@@ -285,4 +292,20 @@ func (hdlr *Handlers) pruneQueuesAndMessages(
 			)
 		}
 	}
+
+	// Prune spent hashcash tokens older than 1 year.
+	hashcashCutoff := time.Now().Add(-spentHashcashTTL)
+
+	pruned, err := hdlr.params.Database.
+		PruneSpentHashcash(ctx, hashcashCutoff)
+	if err != nil {
+		hdlr.log.Error(
+			"spent hashcash pruning failed", "error", err,
+		)
+	} else if pruned > 0 {
+		hdlr.log.Info(
+			"pruned spent hashcash tokens",
+			"deleted", pruned,
+		)
+	}
 }

internal/hashcash/channel.go

@@ -0,0 +1,186 @@
+package hashcash
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+var (
+	errBodyHashMismatch = errors.New(
+		"body hash mismatch",
+	)
+	errBodyHashMissing = errors.New(
+		"body hash missing",
+	)
+)
+
+// ChannelValidator checks hashcash stamps for
+// per-channel PRIVMSG validation. It verifies that
+// stamps are bound to a specific channel and message
+// body. Replay prevention is handled externally via
+// the database spent_hashcash table for persistence
+// across server restarts (1-year TTL).
+type ChannelValidator struct{}
+
+// NewChannelValidator creates a ChannelValidator.
+func NewChannelValidator() *ChannelValidator {
+	return &ChannelValidator{}
+}
+
+// BodyHash computes the hex-encoded SHA-256 hash of a
+// message body for use in hashcash stamp validation.
+func BodyHash(body []byte) string {
+	hash := sha256.Sum256(body)
+
+	return hex.EncodeToString(hash[:])
+}
+
+// ValidateStamp checks a channel hashcash stamp. It
+// verifies the stamp format, difficulty, date, channel
+// binding, body hash binding, and proof-of-work. Replay
+// detection is NOT performed here — callers must check
+// the spent_hashcash table separately.
+//
+// Stamp format: 1:bits:YYMMDD:channel:bodyhash:counter.
+func (cv *ChannelValidator) ValidateStamp(
+	stamp string,
+	requiredBits int,
+	channel string,
+	bodyHash string,
+) error {
+	if requiredBits <= 0 {
+		return nil
+	}
+
+	parts := strings.Split(stamp, ":")
+	if len(parts) != stampFields {
+		return fmt.Errorf(
+			"%w: expected %d, got %d",
+			errInvalidFields, stampFields, len(parts),
+		)
+	}
+
+	version := parts[0]
+	bitsStr := parts[1]
+	dateStr := parts[2]
+	resource := parts[3]
+	stampBodyHash := parts[4]
+
+	headerErr := validateChannelHeader(
+		version, bitsStr, resource,
+		requiredBits, channel,
+	)
+	if headerErr != nil {
+		return headerErr
+	}
+
+	stampTime, parseErr := parseStampDate(dateStr)
+	if parseErr != nil {
+		return parseErr
+	}
+
+	timeErr := validateTime(stampTime)
+	if timeErr != nil {
+		return timeErr
+	}
+
+	bodyErr := validateBodyHash(
+		stampBodyHash, bodyHash,
+	)
+	if bodyErr != nil {
+		return bodyErr
+	}
+
+	return validateProof(stamp, requiredBits)
+}
+
+// StampHash returns a deterministic hash of a stamp
+// string for use as a spent-token key.
+func StampHash(stamp string) string {
+	hash := sha256.Sum256([]byte(stamp))
+
+	return hex.EncodeToString(hash[:])
+}
+
+func validateChannelHeader(
+	version, bitsStr, resource string,
+	requiredBits int,
+	channel string,
+) error {
+	if version != stampVersion {
+		return fmt.Errorf(
+			"%w: %s", errBadVersion, version,
+		)
+	}
+
+	claimedBits, err := strconv.Atoi(bitsStr)
+	if err != nil || claimedBits < requiredBits {
+		return fmt.Errorf(
+			"%w: need %d bits",
+			errInsufficientBits, requiredBits,
+		)
+	}
+
+	if resource != channel {
+		return fmt.Errorf(
+			"%w: got %q, want %q",
+			errWrongResource, resource, channel,
+		)
+	}
+
+	return nil
+}
+
+func validateBodyHash(
+	stampBodyHash, expectedBodyHash string,
+) error {
+	if stampBodyHash == "" {
+		return errBodyHashMissing
+	}
+
+	if stampBodyHash != expectedBodyHash {
+		return fmt.Errorf(
+			"%w: got %q, want %q",
+			errBodyHashMismatch,
+			stampBodyHash, expectedBodyHash,
+		)
+	}
+
+	return nil
+}
+
+// MintChannelStamp computes a channel hashcash stamp
+// with the given difficulty, channel name, and body hash.
+// This is intended for clients to generate stamps before
+// sending PRIVMSG to hashcash-protected channels.
+//
+// Stamp format: 1:bits:YYMMDD:channel:bodyhash:counter.
+func MintChannelStamp(
+	bits int,
+	channel string,
+	bodyHash string,
+) string {
+	date := time.Now().UTC().Format(dateFormatShort)
+	prefix := fmt.Sprintf(
+		"1:%d:%s:%s:%s:",
+		bits, date, channel, bodyHash,
+	)
+
+	counter := uint64(0)
+
+	for {
+		stamp := prefix + strconv.FormatUint(counter, 16)
+		hash := sha256.Sum256([]byte(stamp))
+
+		if hasLeadingZeroBits(hash[:], bits) {
+			return stamp
+		}
+
+		counter++
+	}
+}

internal/hashcash/channel_test.go

@@ -0,0 +1,244 @@
+package hashcash_test
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"testing"
+
+	"git.eeqj.de/sneak/neoirc/internal/hashcash"
+)
+
+const (
+	testChannel  = "#general"
+	testBodyText = `["hello world"]`
+)
+
+func testBodyHash() string {
+	hash := sha256.Sum256([]byte(testBodyText))
+
+	return hex.EncodeToString(hash[:])
+}
+
+func TestChannelValidateHappyPath(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	stamp := hashcash.MintChannelStamp(
+		testBits, testChannel, bodyHash,
+	)
+
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, bodyHash,
+	)
+	if err != nil {
+		t.Fatalf("valid channel stamp rejected: %v", err)
+	}
+}
+
+func TestChannelValidateWrongChannel(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	stamp := hashcash.MintChannelStamp(
+		testBits, testChannel, bodyHash,
+	)
+
+	err := validator.ValidateStamp(
+		stamp, testBits, "#other", bodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected channel mismatch error")
+	}
+}
+
+func TestChannelValidateWrongBodyHash(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	stamp := hashcash.MintChannelStamp(
+		testBits, testChannel, bodyHash,
+	)
+
+	wrongHash := sha256.Sum256([]byte("different body"))
+	wrongBodyHash := hex.EncodeToString(wrongHash[:])
+
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, wrongBodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected body hash mismatch error")
+	}
+}
+
+func TestChannelValidateInsufficientBits(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	// Mint with 2 bits but require 4.
+	stamp := hashcash.MintChannelStamp(
+		testBits, testChannel, bodyHash,
+	)
+
+	err := validator.ValidateStamp(
+		stamp, 4, testChannel, bodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected insufficient bits error")
+	}
+}
+
+func TestChannelValidateZeroBitsSkips(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+
+	err := validator.ValidateStamp(
+		"garbage", 0, "#ch", "abc",
+	)
+	if err != nil {
+		t.Fatalf("zero bits should skip: %v", err)
+	}
+}
+
+func TestChannelValidateBadFormat(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+
+	err := validator.ValidateStamp(
+		"not:valid", testBits, testChannel, "abc",
+	)
+	if err == nil {
+		t.Fatal("expected bad format error")
+	}
+}
+
+func TestChannelValidateBadVersion(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	stamp := "2:2:260317:#general:" + bodyHash + ":counter"
+
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, bodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected bad version error")
+	}
+}
+
+func TestChannelValidateExpiredStamp(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	// Mint with a very old date by manually constructing.
+	stamp := mintStampWithDate(
+		t, testBits, testChannel, "200101",
+	)
+
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, bodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected expired stamp error")
+	}
+}
+
+func TestChannelValidateMissingBodyHash(t *testing.T) {
+	t.Parallel()
+
+	validator := hashcash.NewChannelValidator()
+	bodyHash := testBodyHash()
+
+	// Construct a stamp with empty body hash field.
+	stamp := mintStampWithDate(
+		t, testBits, testChannel, todayDate(),
+	)
+
+	// This uses the session-style stamp which has empty
+	// ext field — body hash is missing.
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, bodyHash,
+	)
+	if err == nil {
+		t.Fatal("expected missing body hash error")
+	}
+}
+
+func TestBodyHash(t *testing.T) {
+	t.Parallel()
+
+	body := []byte(`["hello world"]`)
+	bodyHash := hashcash.BodyHash(body)
+
+	if len(bodyHash) != 64 {
+		t.Fatalf(
+			"expected 64-char hex hash, got %d",
+			len(bodyHash),
+		)
+	}
+
+	// Same input should produce same hash.
+	bodyHash2 := hashcash.BodyHash(body)
+	if bodyHash != bodyHash2 {
+		t.Fatal("body hash not deterministic")
+	}
+
+	// Different input should produce different hash.
+	bodyHash3 := hashcash.BodyHash([]byte("different"))
+	if bodyHash == bodyHash3 {
+		t.Fatal("different inputs produced same hash")
+	}
+}
+
+func TestStampHash(t *testing.T) {
+	t.Parallel()
+
+	hash1 := hashcash.StampHash("stamp1")
+	hash2 := hashcash.StampHash("stamp2")
+
+	if hash1 == hash2 {
+		t.Fatal("different stamps produced same hash")
+	}
+
+	// Same input should be deterministic.
+	hash1b := hashcash.StampHash("stamp1")
+	if hash1 != hash1b {
+		t.Fatal("stamp hash not deterministic")
+	}
+}
+
+func TestMintChannelStamp(t *testing.T) {
+	t.Parallel()
+
+	bodyHash := testBodyHash()
+	stamp := hashcash.MintChannelStamp(
+		testBits, testChannel, bodyHash,
+	)
+
+	if stamp == "" {
+		t.Fatal("expected non-empty stamp")
+	}
+
+	// Validate the minted stamp.
+	validator := hashcash.NewChannelValidator()
+
+	err := validator.ValidateStamp(
+		stamp, testBits, testChannel, bodyHash,
+	)
+	if err != nil {
+		t.Fatalf("minted stamp failed validation: %v", err)
+	}
+}

internal/middleware/middleware.go

@@ -126,18 +126,23 @@ func (mware *Middleware) Logging() func(http.Handler) http.Handler {
 }
 
 // CORS returns middleware that handles Cross-Origin Resource Sharing.
+// AllowCredentials is true so browsers include cookies in
+// cross-origin API requests.
 func (mware *Middleware) CORS() func(http.Handler) http.Handler {
 	return cors.Handler(cors.Options{ //nolint:exhaustruct // optional fields
-		AllowedOrigins: []string{"*"},
+		AllowOriginFunc: func(
+			_ *http.Request, _ string,
+		) bool {
+			return true
+		},
 		AllowedMethods: []string{
 			"GET", "POST", "PUT", "DELETE", "OPTIONS",
 		},
 		AllowedHeaders: []string{
-			"Accept", "Authorization",
-			"Content-Type", "X-CSRF-Token",
+			"Accept", "Content-Type", "X-CSRF-Token",
 		},
 		ExposedHeaders:   []string{"Link"},
-		AllowCredentials: false,
+		AllowCredentials: true,
 		MaxAge:           corsMaxAge,
 	})
 }

internal/server/routes.go

@@ -75,10 +75,6 @@ func (srv *Server) setupAPIv1(router chi.Router) {
 		"/session",
 		srv.handlers.HandleCreateSession(),
 	)
-	router.Post(
-		"/register",
-		srv.handlers.HandleRegister(),
-	)
 	router.Post(
 		"/login",
 		srv.handlers.HandleLogin(),

pkg/irc/commands.go

@@ -11,6 +11,7 @@ const (
 	CmdNames   = "NAMES"
 	CmdNick    = "NICK"
 	CmdNotice  = "NOTICE"
+	CmdPass    = "PASS"
 	CmdPart    = "PART"
 	CmdPing    = "PING"
 	CmdPong    = "PONG"