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

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

@@ -10,9 +10,8 @@ type SessionRequest struct {
 
 // SessionResponse is the response from session creation.
 type SessionResponse struct {
-	ID    int64  `json:"id"`
+	ID   int64  `json:"id"`
-	Nick  string `json:"nick"`
+	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
+// SetPassword sets a bcrypt-hashed password on a session,
-// and returns session ID, client ID, and token.
+// enabling multi-client login via POST /api/v1/login.
-func (database *Database) RegisterUser(
+func (database *Database) SetPassword(
 	ctx context.Context,
-	nick, password string,
+	sessionID int64,
-) (int64, int64, string, error) {
+	password string,
+) error {
 	hash, err := bcrypt.GenerateFromPassword(
 		[]byte(password), bcryptCost,
 	)
 	if err != nil {
-		return 0, 0, "", fmt.Errorf(
+		return fmt.Errorf("hash password: %w", err)
-			"hash password: %w", err,
-		)
 	}
 
-	sessionUUID := uuid.New().String()
+	_, err = database.conn.ExecContext(ctx,
-	clientUUID := uuid.New().String()
+		"UPDATE sessions SET password_hash = ? WHERE id = ?",
-
+		string(hash), sessionID)
-	token, err := generateToken()
 	if err != nil {
-		return 0, 0, "", err
+		return fmt.Errorf("set password: %w", err)
 	}
 
-	now := time.Now()
+	return nil
-
-	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
 }
 
 // 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 :=
+	sessionID, _, _, err :=
-		database.RegisterUser(ctx, "reguser", "password123")
+		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 :=
+	sessionID, _, _, err :=
-		database.RegisterUser(ctx, "dupnick", "password123")
+		database.CreateSession(ctx, "wrongpw")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	_ = regSID
+	err = database.SetPassword(
-	_ = regCID
+		ctx, sessionID, "correctpass",
-	_ = regToken
+	)
-
+	if err != nil {
-	dupSID, dupCID, dupToken, dupErr :=
+		t.Fatal(err)
-		database.RegisterUser(ctx, "dupnick", "other12345")
-	if dupErr == nil {
-		t.Fatal("expected error for duplicate nick")
 	}
 
-	_ = dupSID
+	loginSID, loginCID, loginToken, loginErr :=
-	_ = dupCID
+		database.LoginUser(ctx, "wrongpw", "wrongpass12")
-	_ = dupToken
+	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 :=
+	sessionID, _, _, err :=
-		database.RegisterUser(ctx, "loginuser", "mypassword")
+		database.CreateSession(ctx, "loginuser")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	_ = regSID
+	err = database.SetPassword(
-	_ = regCID
+		ctx, sessionID, "mypassword",
-	_ = regToken
+	)
+	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")
+	cookie, err := request.Cookie(authCookieName)
-	if !strings.HasPrefix(auth, "Bearer ") {
+	if err != nil || cookie.Value == "" {
-		return 0, 0, "", errUnauthorized
-	}
-
-	token := strings.TrimPrefix(auth, "Bearer ")
-	if token == "" {
 		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,
+		"id":   sessionID,
-		"nick":  payload.Nick,
+		"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(
+	hashcashErr := hdlr.validateChannelHashcash(
-		writer, request, command, nick, target, body, chID,
+		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"
@@ -32,15 +33,16 @@ import (
 )
 
 const (
-	commandKey  = "command"
+	commandKey     = "command"
-	bodyKey     = "body"
+	bodyKey        = "body"
-	toKey       = "to"
+	toKey          = "to"
-	statusKey   = "status"
+	statusKey      = "status"
-	privmsgCmd  = "PRIVMSG"
+	privmsgCmd     = "PRIVMSG"
-	joinCmd     = "JOIN"
+	joinCmd        = "JOIN"
-	apiMessages = "/api/v1/messages"
+	apiMessages    = "/api/v1/messages"
-	apiSession  = "/api/v1/session"
+	apiSession     = "/api/v1/session"
-	apiState    = "/api/v1/state"
+	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 != "" {
+	if cookie != "" {
-		request.Header.Set(
+		request.AddCookie(&http.Cookie{ //nolint:exhaustruct // only name+value needed
-			"Authorization", "Bearer "+token,
+			Name:  authCookieName,
-		)
+			Value: cookie,
+		})
 	}
 
 	resp, err := http.DefaultClient.Do(request)
@@ -324,17 +327,19 @@ func (tserver *testServer) createSession(
 		)
 	}
 
-	var result struct {
+	// Drain the body.
-		ID    int64  `json:"id"`
+	_, _ = io.ReadAll(resp.Body)
-		Token string `json:"token"`
+
+	// Extract auth cookie from response.
+	for _, cookie := range resp.Cookies() {
+		if cookie.Name == authCookieName {
+			return cookie.Value
+		}
 	}
 
-	decErr := json.NewDecoder(resp.Body).Decode(&result)
+	tserver.t.Fatal("no auth cookie in response")
-	if decErr != nil {
-		tserver.t.Fatalf("decode session: %v", decErr)
-	}
 
-	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 == "" {
+	if cookie == "" {
-		t.Fatal("expected token")
+		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(
+	// Drain initial messages.
-		t, tserver, "/api/v1/register",
+	_, _ = tserver.pollMessages(token, 0)
-		map[string]string{
+
-			"nick": "shortpw", "password": "short",
+	// 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,
+		)
+	}
+
+	if result[statusKey] != "ok" {
+		t.Fatalf(
+			"expected ok, got %v", result[statusKey],
+		)
+	}
 }
 
-func TestRegisterInvalidNick(t *testing.T) {
+func TestPassCommandShortPassword(t *testing.T) {
 	tserver := newTestServer(t)
+	token := tserver.createSession("shortpw")
 
-	postJSONExpectStatus(
+	// Drain initial messages.
-		t, tserver, "/api/v1/register",
+	_, lastID := tserver.pollMessages(token, 0)
-		map[string]string{
+
-			"nick":     "bad nick!",
+	// Try short password — should fail.
-			"password": "password123",
+	status, _ := tserver.sendCommand(
+		token,
+		map[string]any{
+			commandKey: "PASS",
+			bodyKey:    []string{"short"},
 		},
-		http.StatusBadRequest,
 	)
+	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.
+	// Create session and set password via PASS command.
-	regBody, err := json.Marshal(map[string]string{
+	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 {
+	if resp.StatusCode != http.StatusOK {
-		respBody, _ := io.ReadAll(resp2.Body)
+		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"] == "" {
+			break
-		t.Fatal("expected token in response")
+		}
 	}
 
-	// Verify token works.
+	if loginCookie == "" {
-	token, ok := result["token"].(string)
+		t.Fatal("expected auth cookie from login")
-	if !ok {
-		t.Fatal("token not a string")
 	}
 
-	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{
+	// Create session and set password via PASS command.
-		"nick": "wrongpwuser", "password": "correctpass1",
+	token := tserver.createSession("wrongpwuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: "PASS",
+		bodyKey:    []string{"correctpass1"},
 	})
-	if err != nil {
-		t.Fatal(err)
-	}
 
-	resp, err := doRequest(
+	postJSONExpectStatus(
-		t,
+		t, tserver, "/api/v1/login",
-		http.MethodPost,
+		map[string]string{
-		tserver.url("/api/v1/register"),
+			"nick":     "wrongpwuser",
-		bytes.NewReader(regBody),
+			"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,
+		"id":   sessionID,
-		"nick":  payload.Nick,
+		"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

@@ -36,15 +36,21 @@ 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
+	params          *Params
-	log           *slog.Logger
+	log             *slog.Logger
-	hc            *healthcheck.Healthcheck
+	hc              *healthcheck.Healthcheck
-	broker        *broker.Broker
+	broker          *broker.Broker
-	hashcashVal   *hashcash.Validator
+	hashcashVal     *hashcash.Validator
-	stats         *stats.Tracker
+	channelHashcash *hashcash.ChannelValidator
-	cancelCleanup context.CancelFunc
+	stats           *stats.Tracker
+	cancelCleanup   context.CancelFunc
 }
 
 // New creates a new Handlers instance.
@@ -58,12 +64,13 @@ func New(
 	}
 
 	hdlr := &Handlers{ //nolint:exhaustruct // cancelCleanup set in startCleanup
-		params:      &params,
+		params:          &params,
-		log:         params.Logger.Get(),
+		log:             params.Logger.Get(),
-		hc:          params.Healthcheck,
+		hc:              params.Healthcheck,
-		broker:      broker.New(),
+		broker:          broker.New(),
-		hashcashVal: hashcash.NewValidator(resource),
+		hashcashVal:     hashcash.NewValidator(resource),
-		stats:       params.Stats,
+		channelHashcash: hashcash.NewChannelValidator(),
+		stats:           params.Stats,
 	}
 
 	lifecycle.Append(fx.Hook{
@@ -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",
+			"Accept", "Content-Type", "X-CSRF-Token",
-			"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"