README.md

@@ -802,7 +802,12 @@ comes up, serves pages, and is broken in a way nothing reports.
    proxy's log names it regardless. nginx's default `combined` format already
    logs `$remote_addr`; do not replace it with one that drops the client
    address, and retain those logs as long as you would want to answer a question
-   about traffic.
+   about traffic. That log also records the full request path, so it holds the
+   entrypoint UUID of every event a sender posts. webhooker's own log does not,
+   apart from the line a `log` target writes. Protect the proxy's log as you
+   would the entrypoint URLs themselves: anyone who can read it can post events
+   to every entrypoint in it (see
+   [The entrypoint URL is the authentication secret](#the-entrypoint-url-is-the-authentication-secret)).
 
 ### nginx
 
@@ -828,7 +833,9 @@ server {
     client_max_body_size 1m;
 
     # $remote_addr is the client. webhooker's own log names it, as
-    # clientIP, only while TRUSTED_PROXIES covers this proxy.
+    # clientIP, only while TRUSTED_PROXIES covers this proxy. The
+    # request path in this log holds the entrypoint UUID, so protect
+    # the file like the entrypoint URL itself.
     access_log /var/log/nginx/webhooker.access.log combined;
 
     location / {
@@ -1160,7 +1167,16 @@ What that means for an operator:
 
 - **The URL is a capability, so treat it as a secret.** Keep it out of logs,
   ticket bodies, chat messages and screenshots. Anyone who reads it anywhere can
-  post events as that sender.
+  post events as that sender. Apart from a `log` target's line, webhooker's own
+  log lines never carry the UUID: they name a request to the receiver by the
+  route pattern `/h/{uuid}`, the `webhook request received` line names the
+  entrypoint by its `entrypoint_id`, and the access log keeps only the scheme
+  and host of a `Referer`. A `log` target writes the request's headers as
+  received, so a `Referer` naming the entrypoint URL appears in its line, as it
+  does when a sender has followed a redirect from `http://` to `https://`. The
+  reverse proxy's access log does carry the UUID, in the request path, so it
+  must be protected like the URL itself (see
+  [Deployment behind a reverse proxy](#deployment-behind-a-reverse-proxy)).
 - **Rotating means minting a new entrypoint, not changing a key.** There is no
   way to rotate the UUID in place. To retire one, delete the entrypoint (or
   deactivate it, which answers `410`) and create a new one, then point the
@@ -2422,27 +2438,32 @@ log volume it caps rather than eliminates. A path that names no entrypoint is
 recorded by the handler at `DEBUG`, and the aggregate limiter logs its own
 rejections at `DEBUG` and without the path, so neither appears at all under the
 default level. The per-entrypoint limiter is the loud one: it logs every
-rejection at `WARN` with the request path, which on this route is
-attacker-controlled text. A client hammering a single invented path is served
+rejection at `WARN`, naming the route pattern `/h/{uuid}` rather than the
+request path. A client hammering a single invented path is served
 `RECEIVER_RATE_LIMIT` requests and has the rest of its aggregate budget rejected
 there, so the aggregate limit is what bounds the _number_ of those `WARN` lines
 — to under ten times `RECEIVER_RATE_LIMIT` per minute per client IP, 1080 at the
-defaults, where before it there was no bound at all. Their _width_ is bounded by
-the field budgets below, the same ones the access log spends. The access log is
-bounded by neither limit: every request is recorded once at `INFO`, served or
-rejected alike.
+defaults, where before it there was no bound at all. The access log is bounded
+by neither limit: every request is recorded once at `INFO`, served or rejected
+alike.
 
-What the access log does bound is the _content_ of those lines. A 3xx or 4xx
-response logs the chi route pattern — `/h/{uuid}`, `/user/{username}//`, or the
-literal `(unmatched)` when the request hit no route at all — in place of the
-concrete URL. Those are the outcomes an unauthenticated client can drive for
-free: 404 and 429 on any invented receiver path, a login redirect on any
-invented profile path. Logging the URL there would let a flood write text of its
-own choosing, at a length of its own choosing, into the log. 2xx and 5xx
-responses keep the concrete path — a success resolved against a static route or
-against the operator's own data (on the receiver, against a stored entrypoint
-UUID), and a 5xx is a bug in this service, where the exact path is the evidence
-and no client can provoke one at will.
+What the access log does bound is the _content_ of those lines. On the receiver
+route it logs the route pattern `/h/{uuid}` whatever the status, because the
+concrete path carries the entrypoint UUID, which is the entrypoint's credential
+(see
+[The entrypoint URL is the authentication secret](#the-entrypoint-url-is-the-authentication-secret)).
+A request chi never routed, because it matched no route or because a middleware
+answered it first, logs the literal `(unmatched)` whatever the status. In the
+`dev` environment the CORS middleware answers a preflight that way, so a
+preflight to the receiver does not log its UUID either. On every other route, a
+3xx or 4xx response logs the chi route pattern, such as `/user/{username}//`, in
+place of the concrete URL. Those are the outcomes an unauthenticated client can
+drive for free: a 404 on any invented path, a login redirect on any invented
+profile path. Logging the URL there would let a flood write text of its own
+choosing, at a length of its own choosing, into the log. 2xx and 5xx responses
+keep the concrete path — a success resolved against a static route or against
+the operator's own data, and a 5xx is a bug in this service, where the exact
+path is the evidence and no client can provoke one at will.
 
 The query string is never logged; it is replaced by the fixed marker
 `?(redacted)`. It is client-chosen on every route, and
@@ -2454,6 +2475,11 @@ to, `notice`, which names the line a page shows after an action, and the event
 log's `show`, which picks the events it lists. A query string sent to an
 entrypoint is not lost either: the event stores it, and the event log shows it.
 
+The `referer` field keeps only the scheme and host of the request's `Referer`,
+and logs `(redacted)` for one without them, because its path can be an
+entrypoint URL: a sender that follows the `http://` to `https://` redirect in
+the nginx example sends the URL it was redirected from.
+
 Client-supplied request content does not leave the host by the other route
 either. The Sentry SDK attaches the request to every event it captures,
 independently of the access log, and `SendDefaultPII=false` does not cover all
@@ -2468,9 +2494,10 @@ The same hook rewrites the request URL. The SDK builds it as
 `scheme://host/path` from the concrete path, which on the receiver route is
 `/h/<uuid>` in full — and that UUID is a write capability, not an identifier:
 anyone holding it can post events this service accepts and its targets then
-deliver. A tracker has its own retention, access control and deletion policy, so
-the rule the access log follows above does not carry across that boundary. What
-is sent is the chi route pattern instead: `http://host/h/{uuid}`.
+deliver. What is sent is the chi route pattern instead: `http://host/h/{uuid}`.
+A tracker has its own retention, access control and deletion policy, so the
+pattern is sent on every route, including the 2xx and 5xx responses outside the
+receiver for which the access log keeps the concrete path.
 
 The scheme and the host are kept, and everything else in the URL is discarded
 rather than edited, so a future SDK version that starts appending a query string
@@ -2599,9 +2626,7 @@ than it:
 | ------------------------------------------ | ------- | ------------------- | ------------------------------------------ |
 | `request body exceeds limit` (413)         | `WARN`  | path, method        | yes — `MaxBodySize` precedes `RequireAuth` |
 | `csrf: token validation failed` (403)      | `WARN`  | path, method        | yes — `CSRF` precedes `RequireAuth`        |
-| `... rate limit exceeded` (429)            | `WARN`  | path                | yes, on the receiver                       |
 | `auth middleware: unauthenticated request` | `DEBUG` | path, method        | yes, by definition                         |
-| `entrypoint not found`                     | `DEBUG` | entrypoint UUID     | yes, on the receiver                       |
 | `user not found` / `invalid password`      | `DEBUG` | username            | yes, on the sign-in form                   |
 | `login failure limit exceeded` (429)       | `WARN`  | path                | yes, on the sign-in form                   |
 | `password verification capacity exhausted` | `WARN`  | path                | yes, on the sign-in form                   |
@@ -2629,13 +2654,12 @@ wider of the two handlers spends more on than the client spent sending them.
 Every case holds each line to the 2,560-byte ceiling. That per-line ceiling is
 what the figure above states, and every row establishes it.
 
-Three of the sites go further and bound the whole flood's output — the total
-bytes a run of distinct invented values wrote, which is the shape an operator
-sizing storage cares about. They are `request body exceeds limit`
-(`TestMaxBodySize_FloodOfOversizePathsDoesNotGrowTheLog`),
-`entrypoint not found` and `user not found` (the last two through
-`assertBoundedFlood`). The other rows carry no aggregate assertion; the per-line
-ceiling is what they establish.
+Two of the sites go further and bound the whole flood's output — the total bytes
+a run of distinct invented values wrote, which is the shape an operator sizing
+storage cares about. They are `request body exceeds limit`
+(`TestMaxBodySize_FloodOfOversizePathsDoesNotGrowTheLog`) and `user not found`
+(through `assertBoundedFlood`). The other rows carry no aggregate assertion; the
+per-line ceiling is what they establish.
 
 `internal/logfield/logfield_test.go` measures the per-rune charge against what
 the handlers really emit, over roughly 3,000 code points on each, so an
@@ -2653,7 +2677,7 @@ everything else, so its lines take the level the operator set and the handler
 `internal/logger` selected, and every value it emits is spent through the same
 `internal/logfield` budget. A record-not-found is not logged as an error: it is
 the expected outcome on both of those paths, and each handler already records
-its own miss at `DEBUG` — bounded, per the table above — without the SQL. Slow
+its own miss at `DEBUG`, without the SQL and within the ceiling above. Slow
 statements are kept, at `WARN`, above the same 200 ms threshold GORM used and
 with the statement bounded, because that report is the one thing GORM's logger
 gave an operator that nothing else here does. The adapter orders its cases

internal/handlers/logbound_test.go

@@ -1,19 +1,15 @@
 package handlers_test
 
-// The handler-side half of the log-field audit. Two slog calls in
-// this package reach a value an UNAUTHENTICATED client picks outright
-// and of a length it picks outright:
+// The handler-side half of the log-field audit. The slog calls in
+// this package that reach a value an UNAUTHENTICATED client picks
+// outright, and of a length it picks outright, are the failed-login
+// DEBUG lines, whose username is a form field.
 //
-//   - the unknown-entrypoint DEBUG line on /h/{uuid}, whose
-//     path segment matched no stored entrypoint and so is bounded by
-//     nothing;
-//   - the failed-login DEBUG lines, whose username is a form field.
-//
-// Both are at DEBUG, which is off in production by default. That is
+// They are at DEBUG, which is off in production by default. That is
 // not a bound: an operator turning DEBUG on to diagnose a flood must
-// not thereby hand the flood an unbounded write. Both spend the same
-// internal/logfield budget as the access log, and both are held here
-// to middleware.MaxAccessLogLineBytes.
+// not thereby hand the flood an unbounded write. They spend the same
+// internal/logfield budget as the access log, and are held here to
+// middleware.MaxAccessLogLineBytes.
 //
 // The two login lines past the username lookup — "invalid password"
 // and "user logged in" — carry the same cap without needing it, since
@@ -260,43 +256,6 @@ func postLoginWithPassword(
 	return w.Code
 }
 
-// TestUnknownEntrypoint_LogLineDoesNotTrackPathSize drives 8 KB of
-// client-chosen path at the unauthenticated receiver's
-// unknown-entrypoint DEBUG line and holds it to the same ceiling the
-// access log states.
-func TestUnknownEntrypoint_LogLineDoesNotTrackPathSize(t *testing.T) {
-	t.Parallel()
-
-	for handlerName, newHandler := range logHandlers() {
-		for fillName, fill := range escapeFills() {
-			t.Run(handlerName+"/"+fillName, func(t *testing.T) {
-				t.Parallel()
-
-				h, buf := capturingHandlers(t, newHandler)
-				router := receiverRouter(h)
-
-				for i := range floodRequests {
-					assert.Equal(
-						t,
-						http.StatusNotFound,
-						postReceiver(
-							t, router,
-							oversizedFill(fill)+
-								strings.Repeat("y", i),
-						),
-					)
-				}
-
-				lines := logLines(t, buf)
-				require.Len(t, lines, floodRequests)
-				assertNoClientText(t, buf)
-
-				assertBoundedFlood(t, buf.Len())
-			})
-		}
-	}
-}
-
 // TestFailedLogin_LogLineDoesNotTrackUsernameSize drives 8 KB of
 // client-chosen username at the unauthenticated login endpoint's
 // DEBUG line and holds it to the same ceiling.

internal/handlers/webhook.go

@@ -10,7 +10,6 @@ import (
 	"gorm.io/gorm"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/delivery"
-	"sneak.berlin/go/webhooker/internal/logfield"
 	"sneak.berlin/go/webhooker/internal/middleware"
 )
 
@@ -49,14 +48,13 @@ func (h *Handlers) HandleWebhook() http.HandlerFunc {
 			return
 		}
 
-		// Logged only once the UUID is known to name a real
-		// entrypoint. The UUID comes straight out of the path on
-		// the one unauthenticated endpoint, so logging it before
-		// the lookup let a client write an INFO line per invented
-		// path; the request itself is already in the access log
-		// and a miss is already logged at DEBUG.
+		// Logged only once the lookup has found the entrypoint, so
+		// an invented path writes no INFO line; a miss is logged at
+		// DEBUG. The entrypoint is named by its ID: the UUID is its
+		// credential and is never logged.
 		h.log.Info("webhook request received",
-			"entrypoint_uuid", entrypointUUID,
+			"entrypoint_id", entrypoint.ID,
+			"webhook_id", entrypoint.WebhookID,
 			"method", r.Method,
 			"remoteIP", middleware.RemoteIP(r),
 			"clientIP", middleware.ClientIP(r),
@@ -133,17 +131,10 @@ func (h *Handlers) lookupEntrypoint(
 		"path = ?", entrypointUUID,
 	).First(&entrypoint)
 	if result.Error != nil {
-		// The receiver is unauthenticated and /h/{uuid}
-		// matches any single segment, so this value is entirely
-		// client-chosen on exactly the branch where the lookup
-		// failed. DEBUG is off by default; the cap is what keeps
-		// turning it on from restoring an unbounded write.
-		h.log.Debug(
-			"entrypoint not found",
-			"path", logfield.Truncate(
-				entrypointUUID, logfield.MaxBytes,
-			),
-		)
+		// Not even an unknown UUID is logged. The receiver's log
+		// lines never carry the path segment, which is a credential
+		// whenever it names an entrypoint.
+		h.log.Debug("entrypoint not found")
 		http.NotFound(w, r)
 
 		return entrypoint, false

internal/handlers/webhook_test.go

@@ -12,12 +12,15 @@ import (
 	"testing"
 
 	"github.com/go-chi/chi"
+	"github.com/google/uuid"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"gorm.io/gorm/clause"
 	"sneak.berlin/go/webhooker/internal/config"
 	"sneak.berlin/go/webhooker/internal/database"
 	"sneak.berlin/go/webhooker/internal/handlers"
 	"sneak.berlin/go/webhooker/internal/middleware"
+	"sneak.berlin/go/webhooker/internal/middleware/middlewaretest"
 )
 
 // TestHandleWebhook_LogsClientNextToThePeer checks that the
@@ -99,6 +102,87 @@ func TestHandleWebhook_LogsClientNextToThePeer(t *testing.T) {
 	}
 }
 
+// TestHandleWebhook_LogsNoEntrypointUUID sends an accepted event, a
+// request over the receiver rate limit and a request for an unknown
+// UUID through the receiver as routes.go mounts it, and checks that
+// nothing logged, at any level, carries either UUID.
+func TestHandleWebhook_LogsNoEntrypointUUID(t *testing.T) {
+	t.Parallel()
+
+	var (
+		h  *handlers.Handlers
+		db *database.Database
+	)
+
+	cfg := &config.Config{DataDir: t.TempDir(), ReceiverRateLimit: 1}
+
+	app := newTestAppWithConfig(t, cfg, &h, &db)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	buf := new(bytes.Buffer)
+	log := slog.New(slog.NewJSONHandler(
+		buf, &slog.HandlerOptions{Level: slog.LevelDebug},
+	))
+	h.SetLogForTest(log)
+	mw := middlewaretest.New(t, log, cfg, nil)
+
+	webhook := seedWebhook(t, db)
+	entrypoint := &database.Entrypoint{
+		WebhookID: webhook.ID,
+		Path:      uuid.New().String(),
+		Active:    true,
+	}
+	require.NoError(t, db.DB().Omit(clause.Associations).
+		Create(entrypoint).Error)
+
+	unknownUUID := uuid.New().String()
+
+	router := chi.NewRouter()
+	router.Use(mw.Logging())
+	router.With(mw.ReceiverRateLimit()).HandleFunc(
+		middleware.ReceiverRoute, h.HandleWebhook(),
+	)
+
+	// In order: the limit is one request per minute per path, so the
+	// second request for the known UUID is the rejected one.
+	for _, step := range []struct {
+		entrypointUUID string
+		wantStatus     int
+	}{
+		{entrypoint.Path, http.StatusOK},
+		{entrypoint.Path, http.StatusTooManyRequests},
+		{unknownUUID, http.StatusNotFound},
+	} {
+		req := httptest.NewRequestWithContext(
+			context.Background(), http.MethodPost,
+			"/h/"+step.entrypointUUID, strings.NewReader("{}"),
+		)
+		w := httptest.NewRecorder()
+		router.ServeHTTP(w, req)
+
+		require.Equal(t, step.wantStatus, w.Code)
+	}
+
+	// The lines this test is about were all written, so the checks
+	// below are not passing on an empty log.
+	for _, msg := range []string{
+		"webhook request received",
+		"webhook receiver rate limit exceeded",
+		"entrypoint not found",
+	} {
+		assert.Contains(t, buf.String(), `"msg":"`+msg+`"`)
+	}
+
+	assert.NotContains(t, buf.String(), entrypoint.Path)
+	assert.NotContains(t, buf.String(), unknownUUID)
+
+	line := receivedLine(t, buf)
+	assert.Equal(t, entrypoint.ID, line["entrypoint_id"])
+	assert.Equal(t, webhook.ID, line["webhook_id"])
+}
+
 // receivedLine returns the one "webhook request received" line in the
 // captured JSON log.
 func receivedLine(t *testing.T, buf *bytes.Buffer) map[string]any {

internal/middleware/accesslog_test.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"strings"
 	"testing"
 
@@ -27,6 +28,13 @@ const floodRequests = 64
 // line for a redirected or rejected request may contain it.
 const attackerMarker = "QQATTACKERTEXTQQ"
 
+// knownEntrypointUUID and failingEntrypointUUID are the UUIDs the
+// stand-in receiver in accessLogRouter answers 200 and 500 to.
+const (
+	knownEntrypointUUID   = "6f1e2a9c-4b7d-4e3a-9c2f-1d8b5a7e3c60"
+	failingEntrypointUUID = "0b7c3e5a-2d9f-4a61-8e4b-7c1d6f2a9e35"
+)
+
 // maxLineBytes bounds a single access log line whose client-supplied
 // fields are of ordinary size. Well above what the fixed fields need,
 // well below the length of the oversized input the amplification tests
@@ -132,17 +140,21 @@ func accessLogRouter(m *middleware.Middleware) *chi.Mux {
 	)
 
 	router.HandleFunc(
-		"/h/{uuid}",
+		middleware.ReceiverRoute,
 		func(w http.ResponseWriter, r *http.Request) {
-			// Stands in for the real handler: an unknown entrypoint
-			// UUID 404s, a known one succeeds.
-			if chi.URLParam(r, "uuid") != "known" {
+			// Stands in for the real handler: a known entrypoint
+			// UUID succeeds, a failing one is a server error, and
+			// any other 404s.
+			switch chi.URLParam(r, "uuid") {
+			case knownEntrypointUUID:
+				w.WriteHeader(http.StatusOK)
+			case failingEntrypointUUID:
+				http.Error(
+					w, "boom", http.StatusInternalServerError,
+				)
+			default:
 				http.Error(w, "not found", http.StatusNotFound)
-
-				return
 			}
-
-			w.WriteHeader(http.StatusOK)
 		},
 	)
 
@@ -335,11 +347,13 @@ func oversizedValue(ch string) string {
 }
 
 // oversizedHeaders fills every client-supplied header the access log
-// reads with the same value.
+// reads with the same value. The Referer carries it as the host of an
+// absolute URL, because the access log keeps only a Referer's scheme
+// and host.
 func oversizedHeaders(value string) map[string]string {
 	return map[string]string{
 		"User-Agent":   value,
-		"Referer":      value,
+		"Referer":      "http://" + value,
 		"X-Request-Id": value,
 	}
 }
@@ -649,17 +663,111 @@ func TestAccessLog_SuccessKeepsConcretePathAndRedactsQuery(
 	router := accessLogRouter(m)
 
 	assert.Equal(
-		t, http.StatusOK, get(t, router, "/h/known?src=ci"),
+		t, http.StatusOK,
+		get(t, router, "/.well-known/healthcheck?src=ci"),
 	)
 
-	// The path resolved against a stored entrypoint, so it stays. The
-	// query never does: see TestAccessLog_UnauthenticatedSuccess...
 	entries := accessLogEntries(t, buf)
 	require.Len(t, entries, 1)
-	assert.Equal(t, "/h/known?(redacted)", entries[0]["url"])
+	assert.Equal(
+		t, "/.well-known/healthcheck?(redacted)", entries[0]["url"],
+	)
 	assert.NotContains(t, buf.String(), "src=ci")
 }
 
+// TestAccessLog_ReceiverNeverLogsTheUUID covers the two statuses that
+// keep the concrete path on every other route. On the receiver that
+// path carries the entrypoint UUID, so the line names the route
+// pattern instead.
+func TestAccessLog_ReceiverNeverLogsTheUUID(t *testing.T) {
+	t.Parallel()
+
+	for entrypointUUID, wantStatus := range map[string]int{
+		knownEntrypointUUID:   http.StatusOK,
+		failingEntrypointUUID: http.StatusInternalServerError,
+	} {
+		t.Run(strconv.Itoa(wantStatus), func(t *testing.T) {
+			t.Parallel()
+
+			m, buf := capturingMiddleware(t)
+			router := accessLogRouter(m)
+
+			assert.Equal(
+				t, wantStatus,
+				get(t, router, "/h/"+entrypointUUID+"?src=ci"),
+			)
+
+			entries := accessLogEntries(t, buf)
+			require.Len(t, entries, 1)
+			assert.Equal(t, middleware.ReceiverRoute, entries[0]["url"])
+			assert.NotContains(t, buf.String(), entrypointUUID)
+		})
+	}
+}
+
+// TestAccessLog_ReceiverPreflightNeverLogsTheUUID sends a CORS
+// preflight to the receiver in dev, in the production middleware
+// order. CORS answers it with 200 before chi routes it, so the line
+// names no route and carries no UUID.
+func TestAccessLog_ReceiverPreflightNeverLogsTheUUID(t *testing.T) {
+	t.Parallel()
+
+	m, buf := capturingMiddleware(t)
+
+	router := chi.NewRouter()
+	router.Use(m.Logging())
+	router.Use(m.CORS())
+	router.HandleFunc(
+		middleware.ReceiverRoute,
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.WriteHeader(http.StatusOK)
+		},
+	)
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodOptions,
+		"/h/"+knownEntrypointUUID, nil,
+	)
+	req.Header.Set("Origin", "https://sender.example")
+	req.Header.Set("Access-Control-Request-Method", http.MethodPost)
+
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+	assert.Equal(t, http.StatusOK, w.Code)
+
+	entries := accessLogEntries(t, buf)
+	require.Len(t, entries, 1)
+	assert.Equal(t, unmatchedRouteLiteral, entries[0]["url"])
+	assert.NotContains(t, buf.String(), knownEntrypointUUID)
+}
+
+// TestAccessLog_RefererNeverLogsTheUUID sends receiver requests whose
+// Referer is the entrypoint URL, as a sender's is after it follows a
+// redirect from http:// to https://. The referer field keeps only the
+// scheme and host, and a Referer without them is logged as a marker.
+func TestAccessLog_RefererNeverLogsTheUUID(t *testing.T) {
+	t.Parallel()
+
+	m, buf := capturingMiddleware(t)
+	router := accessLogRouter(m)
+
+	for _, referer := range []string{
+		"http://webhooker.example/h/" + knownEntrypointUUID + "?src=ci",
+		"/h/" + knownEntrypointUUID,
+	} {
+		assert.Equal(t, http.StatusOK, getWithHeaders(
+			t, router, "/h/"+knownEntrypointUUID,
+			map[string]string{"Referer": referer},
+		))
+	}
+
+	entries := accessLogEntries(t, buf)
+	require.Len(t, entries, 2)
+	assert.Equal(t, "http://webhooker.example", entries[0]["referer"])
+	assert.Equal(t, "(redacted)", entries[1]["referer"])
+	assert.NotContains(t, buf.String(), knownEntrypointUUID)
+}
+
 func TestAccessLog_ServerErrorKeepsConcreteURL(t *testing.T) {
 	t.Parallel()
 

internal/middleware/logbound_test.go

@@ -10,8 +10,10 @@ package middleware_test
 //     the client's choosing.
 //   - CSRF's 403 rejection, at WARN, also registered ahead of
 //     RequireAuth.
-//   - The rate limiters' 429 rejection, at WARN, on the
-//     unauthenticated receiver among others.
+//   - The rate limiters' 429 rejection, at WARN. On the receiver
+//     route it names the route pattern rather than the path, and
+//     the limiters that log a path sit behind RequireAuth, so its cap
+//     is defensive.
 //   - RequireAuth's own unauthenticated-request line, at DEBUG.
 //   - RecordLoginFailure's throttle rejection, at WARN. Its cap is
 //     defensive rather than load-bearing today: chi pins the one
@@ -268,10 +270,14 @@ func logSites() map[string]logSite {
 			send:       postNoToken,
 			wantStatus: http.StatusForbidden,
 		},
-		// The per-entrypoint receiver limiter, unauthenticated. Its
-		// bucket is keyed on the path, so the first request through a
-		// fresh path is served and only the ones after it are
-		// rejected; sendUntilLimited absorbs that.
+		// The 429 line every limiter but the aggregate one shares.
+		// Mounted outside any route, as here, it logs the path, as
+		// it does for the limiters behind RequireAuth; on
+		// ReceiverRoute it names the pattern instead. The
+		// per-entrypoint receiver limiter's bucket is keyed on the
+		// path, so the first request through a fresh path is served
+		// and only the ones after it are rejected; sendUntilLimited
+		// absorbs that.
 		"receiver rate limit 429": {
 			build: func(
 				t *testing.T, m *middleware.Middleware,

internal/middleware/metrics.go

@@ -41,7 +41,8 @@ const unmatchedMethod = unmatchedRoute
 // after /h/ is client-chosen, so labelling by path lets any
 // unauthenticated client mint permanent series at will, and publishes
 // the entrypoint UUID (the receiver's only credential) in the scrape
-// while doing it.
+// while doing it. The access log and the 429 line read it for the
+// same reason: see ReceiverRoute.
 //
 // chi populates the route context during routeHTTP, so this is only
 // valid once routing has run. Every caller below is on the recording

internal/middleware/middleware.go

@@ -13,7 +13,6 @@ import (
 	"time"
 
 	basicauth "github.com/99designs/basicauth-go"
-	"github.com/go-chi/chi"
 	"github.com/go-chi/chi/middleware"
 	"github.com/go-chi/cors"
 	"github.com/prometheus/client_golang/prometheus"
@@ -49,6 +48,10 @@ const (
 	// pick the size of the line it writes.
 	redactedQuery = "?(redacted)"
 
+	// redactedReferer stands in for a Referer the access log cannot
+	// reduce to its scheme and host; see accessLogReferer.
+	redactedReferer = "(redacted)"
+
 	// maxLogRequestIDBytes bounds the request id, which is also
 	// client-supplied: chi's RequestID middleware passes an inbound
 	// X-Request-Id header through verbatim. Its generated form is an
@@ -96,14 +99,14 @@ const (
 	// It is also the ceiling on every OTHER line this service writes
 	// THROUGH SLOG that carries text an UNAUTHENTICATED client
 	// supplies. Those lines — the MaxBodySize rejection, the CSRF
-	// rejection, the rate-limit rejection, the unauthenticated-request
-	// and unknown-entrypoint DEBUG lines, the failed-login DEBUG
-	// lines, and the two login-throttle WARN lines ("login failure
-	// limit exceeded" in loginguard.go and "password verification
-	// capacity exhausted" in internal/handlers/auth.go) — spend the
-	// same per-field budgets, and each carries strictly fewer
-	// client-supplied fields than the access log does,
-	// so none of them can reach a width the access log cannot. That is
+	// rejection, the unauthenticated-request DEBUG line, the
+	// failed-login DEBUG lines, and the two login-throttle WARN
+	// lines ("login failure limit exceeded" in loginguard.go and
+	// "password verification capacity exhausted" in
+	// internal/handlers/auth.go) — spend the same per-field budgets,
+	// and each carries strictly fewer client-supplied fields than the
+	// access log does, so none of them can reach a width the access
+	// log cannot. That is
 	// asserted directly, per line and under both handlers, rather than
 	// left to the reasoning: see logbound_test.go in this package and
 	// in internal/handlers.
@@ -151,6 +154,12 @@ const (
 	MaxAccessLogLineBytes = 2560
 )
 
+// ReceiverRoute is the route pattern the webhook receiver is served
+// at. Its path carries the entrypoint UUID, which is the receiver's
+// only credential, so the log lines this package writes name a
+// request on this route by the pattern, never by its path.
+const ReceiverRoute = "/h/{uuid}"
+
 //nolint:revive // MiddlewareParams is a standard fx naming convention.
 type MiddlewareParams struct {
 	fx.In
@@ -268,14 +277,14 @@ func (lrw *loggingResponseWriter) Unwrap() http.ResponseWriter {
 // marker.
 //
 // The path on those branches is bounded by the service's routes or by
-// the operator's data — a 2xx on the receiver means the UUID named a
-// stored entrypoint, a 2xx under /s means the file is in the embedded
-// tree. The query is not bounded by anything: /.well-known/healthcheck
-// and /s/* take no authentication and sit behind no rate limiter, and
-// /pages/login behind only the login limiter, so any of them will
-// answer 200 to a URL carrying an arbitrary number of arbitrary bytes
-// after the '?'. Keeping the path and dropping the query is what makes
-// this branch as bounded as the pattern branches below.
+// the operator's data — a 2xx under /s means the file is in the
+// embedded tree. The query is not bounded by anything:
+// /.well-known/healthcheck and /s/* take no authentication and sit
+// behind no rate limiter, and /pages/login behind only the login
+// limiter, so any of them will answer 200 to a URL carrying an
+// arbitrary number of arbitrary bytes after the '?'. Keeping the path
+// and dropping the query is what makes this branch as bounded as the
+// pattern branches below.
 //
 // Nothing debuggable is lost. The only query parameters the service
 // reads are the login page's `next`, the page to return to,
@@ -297,36 +306,61 @@ func concreteLogURL(r *http.Request) string {
 
 // accessLogURL returns the value for the access log's url field.
 //
-// 2xx and 5xx responses get the concrete path (see concreteLogURL). A
-// success resolved against a static route or against the operator's
-// own data — on the receiver, a 2xx means the UUID named a stored
-// entrypoint — and a server error is our own bug, where the exact URL
-// is the primary evidence and which no client can provoke at will.
+// On ReceiverRoute it is the route pattern whatever the status, so
+// the entrypoint UUID in the path is never logged. A request chi never
+// routed gets unmatchedRoute whatever the status, for the same reason:
+// in dev, CORS answers a preflight to the receiver before routing.
+//
+// On every other route, 2xx and 5xx responses get the concrete path
+// (see concreteLogURL). A success resolved against a static route or
+// against the operator's own data, and a server error is our own bug,
+// where the exact URL is the primary evidence and which no client can
+// provoke at will.
 //
 // 3xx and 4xx responses get the chi route pattern instead. Those are
-// the outcomes an unauthenticated client drives for free: 404 or 429
-// on any invented /h/ path, 303 to the login page on any
-// invented /user/ path. Logging the concrete URL there lets a flood
-// write attacker-chosen text, of attacker-chosen length, into the
-// operator's log at one line per request. The pattern comes from the
-// router's own table, so it is bounded by the service's routes while
-// still naming which class of request was rejected.
+// the outcomes an unauthenticated client drives for free, such as a
+// 303 to the login page on any invented /user/ path. Logging the
+// concrete URL there lets a flood write attacker-chosen text, of
+// attacker-chosen length, into the operator's log at one line per
+// request. The pattern comes from the router's own table, so it is
+// bounded by the service's routes while still naming which class of
+// request was rejected.
 //
 // The pattern is only populated once routing has run, so this must be
 // called after the handler returns, not before.
 func accessLogURL(r *http.Request, status int) string {
+	pattern := routePatternID(r.Context())
+	if pattern == ReceiverRoute || pattern == unmatchedRoute {
+		return pattern
+	}
+
 	if status < http.StatusMultipleChoices ||
 		status >= http.StatusInternalServerError {
 		return concreteLogURL(r)
 	}
 
-	if rc := chi.RouteContext(r.Context()); rc != nil {
-		if pattern := rc.RoutePattern(); pattern != "" {
-			return pattern
-		}
+	return pattern
+}
+
+// accessLogReferer returns the value for the access log's referer
+// field: the Referer's scheme and host, never its path or query. The
+// path can be an entrypoint URL, which carries the UUID: a sender that
+// follows a redirect from http:// to https:// sends the URL it was
+// redirected from, and a browser sends the 404 page's URL under /h/
+// when it fetches that page's stylesheet. A Referer without both a
+// scheme and a host is logged as redactedReferer.
+func accessLogReferer(r *http.Request) string {
+	referer := r.Referer()
+	if referer == "" {
+		return ""
 	}
 
-	return unmatchedRoute
+	parsed, err := url.Parse(referer)
+	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
+		return redactedReferer
+	}
+
+	return parsed.Scheme + "://" + parsed.Host
 }
 
 // Logging returns middleware that logs each HTTP request with
@@ -379,7 +413,7 @@ func (s *Middleware) Logging() func(http.Handler) http.Handler {
 						requestID, maxLogRequestIDBytes,
 					),
 					"referer", logfield.Truncate(
-						r.Referer(), logfield.MaxBytes,
+						accessLogReferer(r), logfield.MaxBytes,
 					),
 					"proto", r.Proto,
 					"remoteIP", RemoteIP(r),

internal/middleware/ratelimit.go

@@ -259,26 +259,28 @@ func (m *Middleware) clientAddr(r *http.Request) (netip.Addr, bool) {
 	return peer, true
 }
 
-// tooManyRequests returns the 429 handler used by the
-// password-change and per-entrypoint receiver limiters: it logs the
+// tooManyRequests returns the 429 handler used by the postRateLimit
+// limiters and the per-entrypoint receiver limiter: it logs the
 // rejection with logMessage and answers with responseMessage.
 // httprate adds the Retry-After header (RFC 6585). The aggregate
 // receiver limiter uses floodTooManyRequests instead.
 //
-// The path is capped against the same budget as the access log's url
-// field. The per-entrypoint receiver limiter is unauthenticated and
-// its path is a client-chosen segment of client-chosen length, so at
-// WARN an uncapped path would let a sender pick the size of the line
-// it writes — the same defect the access log capping closed.
+// On ReceiverRoute the line names the route pattern, so the
+// entrypoint UUID in the path is never logged. Elsewhere it names the
+// path, capped against the same budget as the access log's url field;
+// the limiters there sit behind RequireAuth, so the cap is defensive.
 func (m *Middleware) tooManyRequests(
 	logMessage, responseMessage string,
 ) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
+		path := r.URL.Path
+		if routePatternID(r.Context()) == ReceiverRoute {
+			path = ReceiverRoute
+		}
+
 		m.log.Warn(
 			logMessage,
-			"path", logfield.Truncate(
-				r.URL.Path, logfield.MaxBytes,
-			),
+			"path", logfield.Truncate(path, logfield.MaxBytes),
 			"remoteIP", RemoteIP(r),
 			"clientIP", ClientIP(r),
 		)

internal/server/routes.go

@@ -6,7 +6,8 @@ import (
 
 	sentryhttp "github.com/getsentry/sentry-go/http"
 	"github.com/go-chi/chi"
-	"github.com/go-chi/chi/middleware"
+	chimw "github.com/go-chi/chi/middleware"
+	"sneak.berlin/go/webhooker/internal/middleware"
 	"sneak.berlin/go/webhooker/static"
 )
 
@@ -60,7 +61,7 @@ func (s *Server) SetupRoutes() {
 }
 
 func (s *Server) setupGlobalMiddleware() {
-	s.router.Use(middleware.RequestID)
+	s.router.Use(chimw.RequestID)
 	s.router.Use(s.mw.SecurityHeaders())
 	s.router.Use(s.mw.Logging())
 
@@ -345,7 +346,7 @@ func (s *Server) setupWebhookRoutes() {
 	// unauthenticated endpoint's body; TestReceiver_OversizeBodyRefused
 	// pins it.
 	s.router.With(s.mw.ReceiverRateLimit()).HandleFunc(
-		"/h/{uuid}",
+		middleware.ReceiverRoute,
 		s.h.HandleWebhook(),
 	)
 }