auth: the duplicate-cookie line hides a link's token (audit A4)

Security audit 2026-10-17, finding A4 (low), stage 0. The line logged when
a request carries two unprefixed session cookies printed r.URL.Path raw,
so GET /confirm/<token> wrote the token to the log (reachable only with
PANEL_COOKIE_SECURE=false, where a sibling host can plant the bare name).
loggedPath moves from internal/web to internal/web/auth as LoggedPath
(web imports auth, not the other way) and both lines - the origin check's
refusal and the duplicate-cookie one - go through it.

Tests: TestDuplicateCookieLineHidesALinksToken; TestLoggedPathHidesTokens
moved with the function. go test ./internal/web ./internal/web/auth.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/auth/auth_test.go

@@ -3,9 +3,11 @@ package auth
 import (
 	"database/sql"
 	"errors"
+	"log"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
+	"os"
 	"path/filepath"
 	"strings"
 	"testing"
@@ -88,6 +90,24 @@ func TestSessionTokenRejectsDuplicates(t *testing.T) {
 	}
 }
 
+// The duplicate-cookie line names the request's path, and a link's token is
+// not written to the log with it (audit 2026-10-17, A4).
+func TestDuplicateCookieLineHidesALinksToken(t *testing.T) {
+	m := testModule(t, false)
+	var buf strings.Builder
+	log.SetOutput(&buf)
+	t.Cleanup(func() { log.SetOutput(os.Stderr) })
+	r := httptest.NewRequest(http.MethodGet, "http://panel.example.com/confirm/the-secret-token-of-a-link", nil)
+	r.AddCookie(&http.Cookie{Name: "selfpost_session", Value: "planted-by-a-neighbour"})
+	r.AddCookie(&http.Cookie{Name: "selfpost_session", Value: "the-real-session"})
+	if _, ok := m.sessionToken(r); ok {
+		t.Fatal("duplicate cookies accepted")
+	}
+	if got := buf.String(); strings.Contains(got, "the-secret-token-of-a-link") || !strings.Contains(got, "GET /confirm/… carries 2 cookies") {
+		t.Errorf("logged %q", got)
+	}
+}
+
 func TestSessionTokenReadsOneCookie(t *testing.T) {
 	m := testModule(t, true)
 	r := httptest.NewRequest(http.MethodGet, "http://panel.example.com/domains", nil)

internal/web/auth/handlers.go

@@ -55,7 +55,7 @@ func (m *Module) sessionToken(r *http.Request) (string, bool) {
 		// name cannot be planted that way (see sessionCookiePrefixed).
 		logf("panel: %s %s carries %d cookies named %q — treating the request as signed out; "+
 			"another host on this domain is overwriting the session cookie, clear the cookies for the parent domain",
-			r.Method, r.URL.Path, n, name)
+			r.Method, LoggedPath(r.URL.Path), n, name)
 		return "", false
 	}
 }

internal/web/auth/links.go

@@ -400,3 +400,17 @@ func loginInfo(r *http.Request) string {
 	}
 	return ""
 }
+
+// LoggedPath is a request's path as the log may hold it: the token of a
+// password-reset or confirmation link is a secret, and the log is read by
+// more than the person the link went to (security review, 2026-10-17).
+// Every log line that names a request's path goes through it: the origin
+// check's refusal and the duplicate-cookie line (audit 2026-10-17, A4).
+func LoggedPath(p string) string {
+	for _, prefix := range []string{"/login/reset/", "/confirm/"} {
+		if strings.HasPrefix(p, prefix) && len(p) > len(prefix) {
+			return prefix + "…"
+		}
+	}
+	return p
+}

internal/web/auth/loggedpath_test.go

@@ -0,0 +1,19 @@
+package auth
+
+import "testing"
+
+// A rejected request's path is logged without the token of a link
+// (security review, 2026-10-17).
+func TestLoggedPathHidesTokens(t *testing.T) {
+	for in, want := range map[string]string{
+		"/login/reset/abcDEF123": "/login/reset/…",
+		"/confirm/abcDEF123":     "/confirm/…",
+		"/login/reset":           "/login/reset",
+		"/confirm/":              "/confirm/",
+		"/account/profile":       "/account/profile",
+	} {
+		if got := LoggedPath(in); got != want {
+			t.Errorf("LoggedPath(%q) = %q, want %q", in, got, want)
+		}
+	}
+}