Add inactivity-based session timeout (closes #66 )

Sessions had only a 7-day absolute lifetime, and that cap was enforced only by the cookie's MaxAge -- i.e. only by the browser. An abandoned session stayed usable for the full week. Sessions are now bounded by two independent, server-enforced clocks, and end at whichever expires first: - absolute: created_at + 7 days, stamped once by SetUser and never rewritten, so no amount of activity can extend it - idle: last_seen + SESSION_IDLE_TIMEOUT (default 24h), pushed forward by the new Session.Touch Both deadlines are checked in Session.expired, which IsAuthenticated now consults, so every existing authentication decision honours them without each call site having to remember. Activity means a request that passes RequireAuth, which is the only place Touch is called; an unauthenticated request carrying the cookie cannot keep a session alive. Touch re-checks authentication itself so that guarantee does not depend on the call site. To avoid re-issuing the session cookie on every authenticated request, Touch rewrites last_seen only once it is older than a tenth of the idle window. The session therefore expires up to 10% early relative to the user's true last request, never late. An authenticated session carrying no timestamps (a cookie minted before this change) is treated as expired, so the failure mode of the upgrade is one forced re-login rather than an unbounded session. Tests use an injected clock rather than sleeps and cover idle expiry, refresh on activity, an actively used session still dying at the absolute cap, refusal to refresh unauthenticated or expired sessions, disabled idle expiry, and startup aborting on an unparseable SESSION_IDLE_TIMEOUT.
2026-08-09 05:59:54 +00:00
15 changed files with 928 additions and 682 deletions
--- a/README.md
+++ b/README.md
@@ -92,6 +92,27 @@ TTY detection, and security headers are always applied.
 | `METRICS_USERNAME`      | Basic auth username for `/metrics`  | `""`     |
 | `METRICS_PASSWORD`      | Basic auth password for `/metrics`  | `""`     |
 | `SENTRY_DSN`            | Sentry error reporting DSN          | `""`     |
+| `SESSION_IDLE_TIMEOUT`  | Idle session timeout (Go duration)  | `24h`    |
+
+Sessions are bounded by two independent clocks, and end at whichever
+one runs out first:
+
+- **Idle expiry** (`SESSION_IDLE_TIMEOUT`, default `24h`) is a sliding
+  window. Every authenticated request pushes it forward, so a session
+  in continuous use never hits it, while an abandoned one expires a day
+  after its last use. Set it to `0` to disable idle expiry entirely;
+  the absolute cap below still applies. A set-but-unparseable value
+  aborts startup rather than silently falling back to the default.
+- **Absolute expiry** is a fixed 7 days from login. Activity does
+  **not** extend it: after a week, every session ends and the user
+  authenticates again.
+
+Only requests that authenticate with the session count as activity, so
+an unauthenticated request carrying the cookie cannot keep a session
+alive. The idle timestamp is rewritten at most once per tenth of the
+idle window rather than on every request, which means a session may
+expire up to 10% early relative to the user's true last request, but
+never late.

 On first startup, webhooker automatically generates a cryptographically
 secure session encryption key and stores it in the database. This key
@@ -867,17 +888,9 @@ Applied to all routes in this order:
 8. **Sentry** — Error reporting to Sentry (if `SENTRY_DSN` is set;
   configured with `Repanic: true` so panics still reach Recoverer)

-Additionally, form endpoints (`/pages`, `/user/*`, `/sources`,
-`/source/*`) apply a **MaxBodySize** middleware that limits
-POST/PUT/PATCH request bodies to 1 MB. It is registered ahead of the
-CSRF middleware in every one of those route groups, because
-gorilla/csrf parses the form; if the cap were installed after it, form
-parsing would run under net/http's 10 MB default and the 1 MB limit
-would never apply. A request that declares a `Content-Length` over the
-limit is answered with `413 Request Entity Too Large` before any other
-middleware or handler runs; a chunked request, or one that lies about
-its length, is hard-capped by `http.MaxBytesReader` and fails
-downstream at form-parse time.
+Additionally, form endpoints (`/pages`, `/sources`, `/source/*`) apply a
+**MaxBodySize** middleware that limits POST/PUT/PATCH request bodies to
+1 MB using `http.MaxBytesReader`, preventing oversized form submissions.

 ### Authentication

@@ -899,8 +912,7 @@ downstream at form-parse time.
 - Production security headers on all responses: HSTS, X-Content-Type-Options
  (`nosniff`), X-Frame-Options (`DENY`), Content-Security-Policy, Referrer-Policy,
  and Permissions-Policy
- Request body size limits (1 MB) on all form POST endpoints, enforced
-  by middleware that runs before CSRF parses the form
+- Request body size limits (1 MB) on all form POST endpoints
 - **CSRF protection** via [gorilla/csrf](https://github.com/gorilla/csrf)
  on all state-changing forms (cookie-based double-submit tokens with
  HMAC authentication). Applied to `/pages`, `/sources`, `/source`, and
--- a/TODO.md
+++ b/TODO.md
@@ -28,13 +28,10 @@ databases currently grow without bound.

 # Completed Steps

- 2026-08-09 Enforce the request body size limit before the CSRF
-  middleware parses the form (#90): `MaxBodySize` is now registered
-  ahead of `CSRF()` in every form route group, the `/user/{username}`
-  group gained the cap it never had (which is where `POST /password`
-  lives), the middleware rejects a declared-oversize body with a real
-  413 up front, and the redundant handler-local
-  `http.MaxBytesReader` calls were removed
+- 2026-08-09 Inactivity-based session timeout: sliding idle expiry
+  (`SESSION_IDLE_TIMEOUT`, default `24h`) refreshed on authenticated
+  requests, with the 7-day absolute cap kept as an independent
+  backstop that activity never extends (#66)
 - 2026-08-07 Update golangci-lint to v2.12.2 (Docker image digest in
  `Dockerfile`, release-archive sha256 pins in `script/bootstrap`),
  adopt the canonical `.golangci.yml` (v2 `linters.settings` layout so
@@ -78,7 +75,7 @@ databases currently grow without bound.
    - event redelivery endpoint
    - OpenAPI specification
 - Analytics dashboard: success rates, response times, volume
- Session expiration tuning and a remember-me option
+- A remember-me option at login
 - Password change and reset flow
 - Later, nice to have
    - email delivery target type
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -31,6 +31,10 @@ const (
 	// defaultRetentionSweepInterval is how often the retention
 	// reaper deletes events older than each webhook's RetentionDays.
 	defaultRetentionSweepInterval = time.Hour
+
+	// defaultSessionIdleTimeout is how long a session may go without
+	// authenticated activity before it expires.
+	defaultSessionIdleTimeout = 24 * time.Hour
 )

 // ErrInvalidEnvironment is returned when WEBHOOKER_ENVIRONMENT
@@ -60,6 +64,10 @@ type Config struct {
 	// RetentionSweepInterval is how often the retention reaper runs.
 	RetentionSweepInterval time.Duration

+	// SessionIdleTimeout is the sliding inactivity window after
+	// which a session expires. Non-positive disables idle expiry.
+	SessionIdleTimeout time.Duration
+
 	params *ConfigParams
 	log    *slog.Logger
 }
@@ -162,6 +170,15 @@ func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 		return nil, err
 	}

+	// Same fail-loud treatment for the session idle timeout.
+	sessionIdleTimeout, err := envDuration(
+		"SESSION_IDLE_TIMEOUT",
+		defaultSessionIdleTimeout,
+	)
+	if err != nil {
+		return nil, err
+	}
+
 	// Load configuration values from environment variables
 	s := &Config{
 		DataDir:                envString("DATA_DIR"),
@@ -173,6 +190,7 @@ func New(lc fx.Lifecycle, params ConfigParams) (*Config, error) {
 		Port:                   envInt("PORT", defaultPort),
 		SentryDSN:              envString("SENTRY_DSN"),
 		RetentionSweepInterval: retentionSweepInterval,
+		SessionIdleTimeout:     sessionIdleTimeout,
 		log:                    log,
 		params:                 &params,
 	}
--- a/internal/config/config_test.go
+++ b/internal/config/config_test.go
@@ -163,7 +163,7 @@ func TestRetentionSweepInterval(t *testing.T) {
 			}

 			if tt.expectError {
-				testRetentionSweepIntervalError(t)
+				expectStartupError(t)
 			} else {
 				testRetentionSweepIntervalSuccess(t, tt.expected)
 			}
@@ -171,7 +171,9 @@ func TestRetentionSweepInterval(t *testing.T) {
 	}
 }

-func testRetentionSweepIntervalError(t *testing.T) {
+// expectStartupError asserts that fx refuses to build the app,
+// which is what a set-but-unparseable duration must cause.
+func expectStartupError(t *testing.T) {
 	t.Helper()

 	var cfg *config.Config
@@ -215,6 +217,82 @@ func testRetentionSweepIntervalSuccess(
 	assert.Equal(t, expected, cfg.RetentionSweepInterval)
 }

+func TestSessionIdleTimeout(t *testing.T) {
+	tests := []struct {
+		name        string
+		set         bool
+		value       string
+		expectError bool
+		expected    time.Duration
+	}{
+		{
+			name:     "unset uses default",
+			set:      false,
+			expected: 24 * time.Hour,
+		},
+		{
+			name:     "valid value is parsed",
+			set:      true,
+			value:    "30m",
+			expected: 30 * time.Minute,
+		},
+		{
+			name:        "unparseable value fails startup",
+			set:         true,
+			value:       "not-a-duration",
+			expectError: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			// Cannot use t.Parallel() here because t.Setenv
+			// is incompatible with parallel subtests.
+			t.Setenv("WEBHOOKER_ENVIRONMENT", "dev")
+
+			if tt.set {
+				t.Setenv("SESSION_IDLE_TIMEOUT", tt.value)
+			} else {
+				require.NoError(t, os.Unsetenv(
+					"SESSION_IDLE_TIMEOUT",
+				))
+			}
+
+			if tt.expectError {
+				expectStartupError(t)
+			} else {
+				testSessionIdleTimeoutSuccess(t, tt.expected)
+			}
+		})
+	}
+}
+
+func testSessionIdleTimeoutSuccess(
+	t *testing.T,
+	expected time.Duration,
+) {
+	t.Helper()
+
+	var cfg *config.Config
+
+	app := fxtest.New(
+		t,
+		fx.Provide(
+			globals.New,
+			logger.New,
+			config.New,
+		),
+		fx.Populate(&cfg),
+	)
+	require.NoError(t, app.Err())
+
+	app.RequireStart()
+
+	defer app.RequireStop()
+
+	assert.Equal(t, expected, cfg.SessionIdleTimeout)
+}
+
 func TestDefaultDataDir(t *testing.T) {
 	for _, env := range []string{"", "dev", "prod"} {
 		name := env
--- a/internal/handlers/auth.go
+++ b/internal/handlers/auth.go
@@ -29,8 +29,10 @@ func (h *Handlers) HandleLoginPage() http.HandlerFunc {
 // HandleLoginSubmit handles the login form submission (POST)
 func (h *Handlers) HandleLoginSubmit() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		// Limit request body to prevent memory exhaustion
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<maxBodyShift)
+
+		// Parse form data
 		err := r.ParseForm()
 		if err != nil {
 			h.log.Error("failed to parse form", "error", err)
--- a/internal/handlers/profile.go
+++ b/internal/handlers/profile.go
@@ -31,8 +31,9 @@ func (h *Handlers) HandlePasswordChange() http.HandlerFunc {
 			return
 		}

-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		// Limit request body to prevent memory exhaustion.
+		r.Body = http.MaxBytesReader(w, r.Body, 1<<maxBodyShift)
+
 		err := r.ParseForm()
 		if err != nil {
 			h.log.Error("failed to parse form", "error", err)
--- a/internal/handlers/source_management.go
+++ b/internal/handlers/source_management.go
@@ -127,8 +127,10 @@ func (h *Handlers) HandleSourceCreateSubmit() http.HandlerFunc {
 			return
 		}

-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		r.Body = http.MaxBytesReader(
+			w, r.Body, 1<<maxBodyShift,
+		)
+
 		err := r.ParseForm()
 		if err != nil {
 			http.Error(
@@ -384,8 +386,10 @@ func (h *Handlers) HandleSourceEditSubmit() http.HandlerFunc {
 			return
 		}

-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		r.Body = http.MaxBytesReader(
+			w, r.Body, 1<<maxBodyShift,
+		)
+
 		err = r.ParseForm()
 		if err != nil {
 			http.Error(
@@ -405,8 +409,10 @@ func (h *Handlers) applyWebhookEdit(
 	r *http.Request,
 	webhook *database.Webhook,
 ) {
-	// The body size cap is enforced by the MaxBodySize middleware,
-	// which runs before CSRF parses the form.
+	r.Body = http.MaxBytesReader(
+		w, r.Body, 1<<maxBodyShift,
+	)
+
 	name := r.FormValue("name")
 	if name == "" {
 		data := map[string]any{
@@ -719,8 +725,10 @@ func (h *Handlers) HandleEntrypointCreate() http.HandlerFunc {
 			return
 		}

-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		r.Body = http.MaxBytesReader(
+			w, r.Body, 1<<maxBodyShift,
+		)
+
 		err = r.ParseForm()
 		if err != nil {
 			http.Error(
@@ -777,8 +785,10 @@ func (h *Handlers) HandleTargetCreate() http.HandlerFunc {
 			return
 		}

-		// The body size cap is enforced by the MaxBodySize
-		// middleware, which runs before CSRF parses the form.
+		r.Body = http.MaxBytesReader(
+			w, r.Body, 1<<maxBodyShift,
+		)
+
 		err = r.ParseForm()
 		if err != nil {
 			http.Error(
@@ -798,8 +808,10 @@ func (h *Handlers) processTargetCreate(
 	r *http.Request,
 	webhook database.Webhook,
 ) {
-	// The body size cap is enforced by the MaxBodySize middleware,
-	// which runs before CSRF parses the form.
+	r.Body = http.MaxBytesReader(
+		w, r.Body, 1<<maxBodyShift,
+	)
+
 	name := r.FormValue("name")
 	targetType := database.TargetType(r.FormValue("type"))
 	targetURL := r.FormValue("url")
--- a/internal/middleware/middleware.go
+++ b/internal/middleware/middleware.go
@@ -186,6 +186,10 @@ func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 				return
 			}

+			// IsAuthenticated also enforces both session expiry
+			// deadlines, so an idle-expired or absolutely-expired
+			// session lands here and is sent back to the login
+			// page.
 			if !s.session.IsAuthenticated(sess) {
 				s.log.Debug(
 					"auth middleware: unauthenticated request",
@@ -199,6 +203,26 @@ func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
 				return
 			}

+			// This request authenticated with the session, so it
+			// counts as activity: push the idle deadline forward.
+			// This is the only place sessions are refreshed, which
+			// is what keeps an unauthenticated request from
+			// extending someone else's session. Touch advances the
+			// idle clock only -- the absolute cap is untouched --
+			// and reports false when nothing changed, so most
+			// requests do not re-issue the cookie. Save before the
+			// handler runs, while the headers are still ours to
+			// write.
+			if s.session.Touch(sess) {
+				err = s.session.Save(r, w, sess)
+				if err != nil {
+					s.log.Error(
+						"auth middleware: failed to refresh session",
+						"error", err,
+					)
+				}
+			}
+
 			next.ServeHTTP(w, r)
 		})
 	}
@@ -285,36 +309,10 @@ func (s *Middleware) NoCache() func(http.Handler) http.Handler {
 	}
 }

-// bodyLimitedMethod reports whether the request method carries a
-// body that the MaxBodySize middleware should cap.
-func bodyLimitedMethod(method string) bool {
-	return method == http.MethodPost ||
-		method == http.MethodPut ||
-		method == http.MethodPatch
-}
-
-// MaxBodySize returns middleware that limits the size of
-// POST/PUT/PATCH request bodies to maxBytes. It must be registered
-// before any middleware that parses the body — notably CSRF, which
-// calls r.PostFormValue — so that form parsing happens under this
-// cap rather than net/http's 10 MB default.
-//
-// Two enforcement paths exist, because http.MaxBytesReader alone
-// cannot produce a 413: it reports the overflow as an error from
-// Read, by which point the body parser downstream has already
-// converted that error into its own response.
-//
-//   - Declared oversize: the request announces a Content-Length
-//     greater than maxBytes. The middleware answers 413 Request
-//     Entity Too Large immediately and does not call the next
-//     handler, so neither CSRF nor the endpoint handler runs.
-//   - Undeclared oversize: the request is chunked (Content-Length
-//     of -1) or lies about its Content-Length. There is nothing to
-//     check up front, so http.MaxBytesReader hard-caps the body at
-//     maxBytes and the request fails downstream — the form parse
-//     errors out and CSRF rejects it with 403. The response is less
-//     precise than a 413, but the body is still never buffered
-//     beyond the cap, which is the property that matters.
+// MaxBodySize returns middleware that limits the request body size
+// for POST requests. If the body exceeds the given limit in
+// bytes, the server returns 413 Request Entity Too Large. This
+// prevents clients from sending arbitrarily large form bodies.
 func (s *Middleware) MaxBodySize(
 	maxBytes int64,
 ) func(http.Handler) http.Handler {
@@ -323,31 +321,14 @@ func (s *Middleware) MaxBodySize(
 			w http.ResponseWriter,
 			r *http.Request,
 		) {
-			if !bodyLimitedMethod(r.Method) {
-				next.ServeHTTP(w, r)
-
-				return
-			}
-
-			if r.ContentLength > maxBytes {
-				s.log.Warn(
-					"request body exceeds limit",
-					"method", r.Method,
-					"path", r.URL.Path,
-					"content_length", r.ContentLength,
-					"limit", maxBytes,
+			if r.Method == http.MethodPost ||
+				r.Method == http.MethodPut ||
+				r.Method == http.MethodPatch {
+				r.Body = http.MaxBytesReader(
+					w, r.Body, maxBytes,
 				)
-				http.Error(
-					w,
-					"Request Entity Too Large",
-					http.StatusRequestEntityTooLarge,
-				)
-
-				return
 			}

-			r.Body = http.MaxBytesReader(w, r.Body, maxBytes)
-
 			next.ServeHTTP(w, r)
 		})
 	}
--- a/internal/middleware/middleware_test.go
+++ b/internal/middleware/middleware_test.go
@@ -3,13 +3,12 @@ package middleware_test
 import (
 	"context"
 	"encoding/base64"
-	"io"
 	"log/slog"
 	"net/http"
 	"net/http/httptest"
 	"os"
-	"strings"
 	"testing"
+	"time"

 	"github.com/gorilla/sessions"
 	"github.com/stretchr/testify/assert"
@@ -30,6 +29,22 @@ func testMiddleware(
 ) (*middleware.Middleware, *session.Session) {
 	t.Helper()

+	m, s, _ := testMiddlewareWithSessionClock(t, env, 0, nil)
+
+	return m, s
+}
+
+// testMiddlewareWithSessionClock is testMiddleware with a
+// configurable session idle timeout and a manually advanced clock,
+// for the session-expiry tests. A nil clock uses the real one.
+func testMiddlewareWithSessionClock(
+	t *testing.T,
+	env string,
+	idleTimeout time.Duration,
+	clock *fakeClock,
+) (*middleware.Middleware, *session.Session, *fakeClock) {
+	t.Helper()
+
 	log := slog.New(slog.NewTextHandler(
 		os.Stderr,
 		&slog.HandlerOptions{Level: slog.LevelDebug},
@@ -37,6 +52,7 @@ func testMiddleware(

 	cfg := &config.Config{
 		Environment:        env,
+		SessionIdleTimeout: idleTimeout,
 	}

 	// Create a real session manager with a known key
@@ -55,11 +71,40 @@ func testMiddleware(
 		SameSite: http.SameSiteLaxMode,
 	}

-	sessManager := session.NewForTest(store, cfg, log, key)
+	var now func() time.Time
+
+	if clock != nil {
+		now = clock.Now
+	}
+
+	sessManager := session.NewForTest(store, cfg, log, key, now)

 	m := middleware.NewForTest(log, cfg, sessManager)

-	return m, sessManager
+	return m, sessManager, clock
+}
+
+// fakeClock is a manually advanced clock, so session expiry can be
+// tested without sleeping.
+type fakeClock struct {
+	t time.Time
+}
+
+func (c *fakeClock) Now() time.Time {
+	return c.t
+}
+
+func (c *fakeClock) Advance(d time.Duration) {
+	c.t = c.t.Add(d)
+}
+
+// newFakeClock returns a clock started at a fixed instant.
+func newFakeClock() *fakeClock {
+	return &fakeClock{
+		t: time.Date(
+			2026, time.January, 2, 3, 4, 5, 0, time.UTC,
+		),
+	}
 }

 // --- Logging Middleware Tests ---
@@ -389,6 +434,181 @@ func TestRequireAuth_UnauthenticatedSession_RedirectsToLogin(
 	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
 }

+// --- RequireAuth Session Expiry Tests ---
+
+// loginCookies authenticates a new session and returns the cookies
+// a browser would then send back.
+func loginCookies(
+	t *testing.T,
+	sessManager *session.Session,
+) []*http.Cookie {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/login", nil)
+	w := httptest.NewRecorder()
+
+	sess, err := sessManager.Get(req)
+	require.NoError(t, err)
+	sessManager.SetUser(sess, "user-123", "testuser")
+	require.NoError(t, sessManager.Save(req, w, sess))
+
+	cookies := w.Result().Cookies()
+	require.NotEmpty(t, cookies, "session cookie should be set")
+
+	return cookies
+}
+
+// runAuthed sends a request carrying cookies through RequireAuth
+// and reports whether the protected handler ran, plus the response.
+func runAuthed(
+	t *testing.T,
+	m *middleware.Middleware,
+	cookies []*http.Cookie,
+) (bool, *httptest.ResponseRecorder) {
+	t.Helper()
+
+	var called bool
+
+	handler := m.RequireAuth()(http.HandlerFunc(
+		func(_ http.ResponseWriter, _ *http.Request) {
+			called = true
+		},
+	))
+
+	req := httptest.NewRequestWithContext(
+		context.Background(),
+		http.MethodGet, "/dashboard", nil,
+	)
+
+	for _, c := range cookies {
+		req.AddCookie(c)
+	}
+
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	return called, w
+}
+
+// sessionCookies filters a response's cookies down to the session
+// cookie, so tests can tell whether the session was re-issued.
+func sessionCookies(
+	w *httptest.ResponseRecorder,
+) []*http.Cookie {
+	var out []*http.Cookie
+
+	for _, c := range w.Result().Cookies() {
+		if c.Name == session.SessionName {
+			out = append(out, c)
+		}
+	}
+
+	return out
+}
+
+func TestRequireAuth_IdleExpiredSession_RedirectsToLogin(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	idle := time.Hour
+
+	m, sessManager, clock := testMiddlewareWithSessionClock(
+		t, config.EnvironmentDev, idle, newFakeClock(),
+	)
+
+	cookies := loginCookies(t, sessManager)
+
+	clock.Advance(idle)
+
+	called, w := runAuthed(t, m, cookies)
+
+	assert.False(
+		t, called,
+		"handler should not run for an idle-expired session",
+	)
+	assert.Equal(t, http.StatusSeeOther, w.Code)
+	assert.Equal(t, "/pages/login", w.Header().Get("Location"))
+	assert.Empty(
+		t, sessionCookies(w),
+		"an expired session must not be refreshed",
+	)
+}
+
+func TestRequireAuth_RefreshesIdleDeadlineOnActivity(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	idle := time.Hour
+
+	m, sessManager, clock := testMiddlewareWithSessionClock(
+		t, config.EnvironmentDev, idle, newFakeClock(),
+	)
+
+	cookies := loginCookies(t, sessManager)
+
+	// Activity halfway through the idle window.
+	clock.Advance(idle / 2)
+
+	called, w := runAuthed(t, m, cookies)
+	require.True(t, called, "handler should run while valid")
+
+	refreshed := sessionCookies(w)
+	require.NotEmpty(
+		t, refreshed,
+		"activity should re-issue the session cookie",
+	)
+
+	// Past the original deadline. The refreshed cookie is still
+	// good; the original one is not.
+	clock.Advance(idle - time.Second)
+
+	calledRefreshed, _ := runAuthed(t, m, refreshed)
+	assert.True(
+		t, calledRefreshed,
+		"refreshed session should outlive the original deadline",
+	)
+
+	calledStale, staleW := runAuthed(t, m, cookies)
+	assert.False(
+		t, calledStale,
+		"the pre-refresh cookie carries the old idle deadline",
+	)
+	assert.Equal(t, http.StatusSeeOther, staleW.Code)
+}
+
+func TestRequireAuth_UnauthenticatedRequestDoesNotRefresh(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	m, sessManager, _ := testMiddlewareWithSessionClock(
+		t, config.EnvironmentDev, time.Hour, newFakeClock(),
+	)
+
+	// A session cookie that exists but was never authenticated.
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/setup", nil)
+	setupW := httptest.NewRecorder()
+
+	sess, err := sessManager.Get(req)
+	require.NoError(t, err)
+	require.NoError(t, sessManager.Save(req, setupW, sess))
+
+	cookies := setupW.Result().Cookies()
+	require.NotEmpty(t, cookies)
+
+	called, w := runAuthed(t, m, cookies)
+
+	assert.False(t, called)
+	assert.Empty(
+		t, sessionCookies(w),
+		"an unauthenticated request must not stamp the session",
+	)
+}
+
 // --- NoCache Middleware Tests ---

 func TestNoCache_SetsHeaders(t *testing.T) {
@@ -428,153 +648,6 @@ func TestNoCache_SetsHeaders(t *testing.T) {
 	)
 }

-// --- MaxBodySize Middleware Tests ---
-
-const testBodyLimit int64 = 64
-
-// maxBodySizeHandler wraps a sentinel handler in MaxBodySize with
-// testBodyLimit. The sentinel records whether it ran and how much of
-// the body it managed to read, so tests can distinguish "never
-// reached" from "reached but truncated".
-type maxBodySizeResult struct {
-	called   bool
-	read     int
-	readErr  error
-	response *httptest.ResponseRecorder
-}
-
-func runMaxBodySize(
-	t *testing.T,
-	req *http.Request,
-) *maxBodySizeResult {
-	t.Helper()
-
-	m, _ := testMiddleware(t, config.EnvironmentDev)
-	res := &maxBodySizeResult{response: httptest.NewRecorder()}
-
-	handler := m.MaxBodySize(testBodyLimit)(http.HandlerFunc(
-		func(w http.ResponseWriter, r *http.Request) {
-			res.called = true
-
-			body, err := io.ReadAll(r.Body)
-			res.read = len(body)
-			res.readErr = err
-
-			w.WriteHeader(http.StatusOK)
-		},
-	))
-
-	handler.ServeHTTP(res.response, req)
-
-	return res
-}
-
-// postWithBody builds a POST request whose Content-Length is
-// accurate for the given payload size.
-func postWithBody(size int) *http.Request {
-	req := httptest.NewRequestWithContext(
-		context.Background(),
-		http.MethodPost, "/pages/login",
-		strings.NewReader(strings.Repeat("a", size)),
-	)
-	req.Header.Set(
-		"Content-Type", "application/x-www-form-urlencoded",
-	)
-
-	return req
-}
-
-func TestMaxBodySize_DeclaredOversize_413AndHandlerNotReached(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	res := runMaxBodySize(t, postWithBody(int(testBodyLimit)+1))
-
-	assert.False(
-		t, res.called,
-		"handler must not be reached for an oversized body",
-	)
-	assert.Equal(
-		t, http.StatusRequestEntityTooLarge, res.response.Code,
-	)
-}
-
-func TestMaxBodySize_AtLimit_PassesThrough(t *testing.T) {
-	t.Parallel()
-
-	res := runMaxBodySize(t, postWithBody(int(testBodyLimit)))
-
-	assert.True(
-		t, res.called,
-		"handler should be reached for a body at the limit",
-	)
-	require.NoError(t, res.readErr)
-	assert.Equal(t, int(testBodyLimit), res.read)
-	assert.Equal(t, http.StatusOK, res.response.Code)
-}
-
-func TestMaxBodySize_UnderLimit_PassesThrough(t *testing.T) {
-	t.Parallel()
-
-	res := runMaxBodySize(t, postWithBody(1))
-
-	assert.True(t, res.called)
-	require.NoError(t, res.readErr)
-	assert.Equal(t, 1, res.read)
-	assert.Equal(t, http.StatusOK, res.response.Code)
-}
-
-func TestMaxBodySize_GetWithOversizeBody_NotCapped(t *testing.T) {
-	t.Parallel()
-
-	req := httptest.NewRequestWithContext(
-		context.Background(),
-		http.MethodGet, "/pages/login",
-		strings.NewReader(
-			strings.Repeat("a", int(testBodyLimit)+1),
-		),
-	)
-
-	res := runMaxBodySize(t, req)
-
-	assert.True(
-		t, res.called,
-		"GET requests are not subject to the POST body cap",
-	)
-	require.NoError(t, res.readErr)
-	assert.Equal(t, int(testBodyLimit)+1, res.read)
-}
-
-// TestMaxBodySize_UndeclaredOversize_TruncatedAtCap covers the
-// chunked / lying-Content-Length case: there is nothing to check up
-// front, so the request reaches the handler but MaxBytesReader
-// hard-caps the body and the read fails at the limit.
-func TestMaxBodySize_UndeclaredOversize_TruncatedAtCap(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	req := postWithBody(int(testBodyLimit) + 1)
-	// Simulate a chunked request: no declared length.
-	req.ContentLength = -1
-
-	res := runMaxBodySize(t, req)
-
-	assert.True(
-		t, res.called,
-		"an undeclared oversize body cannot be rejected up front",
-	)
-	require.Error(
-		t, res.readErr,
-		"reading past the cap must fail",
-	)
-	assert.Equal(
-		t, int(testBodyLimit), res.read,
-		"the handler must not see more than the cap",
-	)
-}
-
 // --- Helper Tests ---

 func TestIpFromHostPort(t *testing.T) {
@@ -628,7 +701,7 @@ func metricsAuthMiddleware(
 	store := sessions.NewCookieStore(key)
 	store.Options = &sessions.Options{Path: "/", MaxAge: 86400}

-	sessManager := session.NewForTest(store, cfg, log, key)
+	sessManager := session.NewForTest(store, cfg, log, key, nil)

 	return middleware.NewForTest(log, cfg, sessManager)
 }
--- a/internal/server/export_test.go
+++ b/internal/server/export_test.go
@@ -1,36 +0,0 @@
-package server
-
-import (
-	"log/slog"
-	"net/http"
-
-	"sneak.berlin/go/webhooker/internal/config"
-	"sneak.berlin/go/webhooker/internal/handlers"
-	"sneak.berlin/go/webhooker/internal/middleware"
-)
-
-// MaxFormBodySizeForTest exposes the form body cap so tests can
-// build requests that sit exactly at, below, and above it.
-const MaxFormBodySizeForTest = maxFormBodySize
-
-// NewRouterForTest builds the real route tree via SetupRoutes with
-// the supplied middleware and handlers, bypassing the fx lifecycle
-// and the HTTP listener. Tests use it so that route-group middleware
-// registration order is exercised exactly as it ships, rather than
-// against a hand-rebuilt chain that could drift from routes.go.
-func NewRouterForTest(
-	log *slog.Logger,
-	cfg *config.Config,
-	mw *middleware.Middleware,
-	h *handlers.Handlers,
-) http.Handler {
-	s := &Server{
-		log:    log,
-		mw:     mw,
-		h:      h,
-		params: ServerParams{Config: cfg},
-	}
-	s.SetupRoutes()
-
-	return s.router
-}
--- a/internal/server/routes.go
+++ b/internal/server/routes.go
@@ -90,11 +90,9 @@ func (s *Server) setupRoutes() {

 func (s *Server) setupPageRoutes() {
 	s.router.Route("/pages", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
-		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
+		r.Use(s.mw.MaxBodySize(maxFormBodySize))

 		r.Group(func(r chi.Router) {
 			r.Use(s.mw.LoginRateLimit())
@@ -108,9 +106,6 @@ func (s *Server) setupPageRoutes() {

 func (s *Server) setupUserRoutes() {
 	s.router.Route("/user/{username}", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
-		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
@@ -123,24 +118,20 @@ func (s *Server) setupUserRoutes() {

 func (s *Server) setupSourceRoutes() {
 	s.router.Route("/sources", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
-		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
+		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Get("/", s.h.HandleSourceList())
 		r.Get("/new", s.h.HandleSourceCreate())
 		r.Post("/new", s.h.HandleSourceCreateSubmit())
 	})

 	s.router.Route("/source/{sourceID}", func(r chi.Router) {
-		// MaxBodySize must precede CSRF: gorilla/csrf parses the
-		// form, so the cap has to be installed before it runs.
-		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Use(s.mw.CSRF())
 		r.Use(s.mw.NoCache())
 		r.Use(s.mw.RequireAuth())
+		r.Use(s.mw.MaxBodySize(maxFormBodySize))
 		r.Get("/", s.h.HandleSourceDetail())
 		r.Get("/edit", s.h.HandleSourceEdit())
 		r.Post("/edit", s.h.HandleSourceEditSubmit())
--- a/internal/server/routes_test.go
+++ b/internal/server/routes_test.go
@@ -1,375 +0,0 @@
-package server_test
-
-import (
-	"context"
-	"html"
-	"net/http"
-	"net/http/httptest"
-	"net/url"
-	"regexp"
-	"strings"
-	"testing"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-	"go.uber.org/fx"
-	"go.uber.org/fx/fxtest"
-	"sneak.berlin/go/webhooker/internal/config"
-	"sneak.berlin/go/webhooker/internal/database"
-	"sneak.berlin/go/webhooker/internal/delivery"
-	"sneak.berlin/go/webhooker/internal/globals"
-	"sneak.berlin/go/webhooker/internal/handlers"
-	"sneak.berlin/go/webhooker/internal/healthcheck"
-	"sneak.berlin/go/webhooker/internal/logger"
-	"sneak.berlin/go/webhooker/internal/middleware"
-	"sneak.berlin/go/webhooker/internal/server"
-	"sneak.berlin/go/webhooker/internal/session"
-)
-
-// csrfCookieName is the cookie gorilla/csrf issues when it runs. Its
-// presence or absence on a response is how these tests tell whether
-// the CSRF middleware executed.
-const csrfCookieName = "_gorilla_csrf"
-
-type noopNotifier struct{}
-
-func (n *noopNotifier) Notify([]delivery.Task) {}
-
-// testEnv is the real router from routes.go plus the collaborators
-// tests need to seed users and forge sessions.
-type testEnv struct {
-	router http.Handler
-	sess   *session.Session
-	db     *database.Database
-}
-
-// newTestEnv wires the dependency graph with fx and builds the
-// production route tree, so middleware registration order is
-// exercised exactly as it ships.
-func newTestEnv(t *testing.T) *testEnv {
-	t.Helper()
-
-	var (
-		log  *logger.Logger
-		cfg  *config.Config
-		mw   *middleware.Middleware
-		hnd  *handlers.Handlers
-		sess *session.Session
-		db   *database.Database
-	)
-
-	app := fxtest.New(
-		t,
-		fx.Provide(
-			globals.New,
-			logger.New,
-			func() *config.Config {
-				return &config.Config{
-					DataDir:     t.TempDir(),
-					Environment: config.EnvironmentDev,
-				}
-			},
-			database.New,
-			database.NewWebhookDBManager,
-			healthcheck.New,
-			session.New,
-			func() delivery.Notifier { return &noopNotifier{} },
-			middleware.New,
-			handlers.New,
-		),
-		fx.Populate(&log, &cfg, &mw, &hnd, &sess, &db),
-	)
-	app.RequireStart()
-	t.Cleanup(app.RequireStop)
-
-	return &testEnv{
-		router: server.NewRouterForTest(log.Get(), cfg, mw, hnd),
-		sess:   sess,
-		db:     db,
-	}
-}
-
-// oversizeValue returns a form value one byte past the route-group
-// body cap, so an encoded form containing it is guaranteed oversize.
-func oversizeValue() string {
-	return strings.Repeat("a", int(server.MaxFormBodySizeForTest)+1)
-}
-
-// csrfCookieSet reports whether the response issued a gorilla/csrf
-// cookie, which only happens if the CSRF middleware ran.
-func csrfCookieSet(w *httptest.ResponseRecorder) bool {
-	for _, c := range w.Result().Cookies() {
-		if c.Name == csrfCookieName {
-			return true
-		}
-	}
-
-	return false
-}
-
-// get issues a GET through the router with the supplied cookies.
-func (e *testEnv) get(
-	path string,
-	cookies []*http.Cookie,
-) *httptest.ResponseRecorder {
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodGet, path, nil,
-	)
-
-	for _, c := range cookies {
-		req.AddCookie(c)
-	}
-
-	w := httptest.NewRecorder()
-	e.router.ServeHTTP(w, req)
-
-	return w
-}
-
-// post issues a urlencoded form POST through the router. The body is
-// a strings.Reader, so the request carries an accurate
-// Content-Length — the signal MaxBodySize checks up front.
-func (e *testEnv) post(
-	path string,
-	form url.Values,
-	cookies []*http.Cookie,
-) *httptest.ResponseRecorder {
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodPost, path,
-		strings.NewReader(form.Encode()),
-	)
-	req.Header.Set(
-		"Content-Type", "application/x-www-form-urlencoded",
-	)
-
-	for _, c := range cookies {
-		req.AddCookie(c)
-	}
-
-	w := httptest.NewRecorder()
-	e.router.ServeHTTP(w, req)
-
-	return w
-}
-
-// csrfFrom renders the page at path and returns the CSRF token from
-// its form together with every cookie needed for the follow-up POST.
-func (e *testEnv) csrfFrom(
-	t *testing.T,
-	path string,
-	cookies []*http.Cookie,
-) (string, []*http.Cookie) {
-	t.Helper()
-
-	w := e.get(path, cookies)
-	require.Equal(t, http.StatusOK, w.Code)
-
-	pattern := regexp.MustCompile(
-		`name="csrf_token" value="([^"]+)"`,
-	)
-
-	match := pattern.FindStringSubmatch(w.Body.String())
-	require.Len(t, match, 2, "form must embed a CSRF token")
-
-	// html/template escapes "+" and "=" in attribute values, and
-	// gorilla/csrf tokens are standard base64, so the value read
-	// out of the markup has to be unescaped before it is submitted.
-	token := html.UnescapeString(match[1])
-
-	combined := make([]*http.Cookie, 0, len(cookies))
-	combined = append(combined, cookies...)
-	combined = append(combined, w.Result().Cookies()...)
-
-	return token, combined
-}
-
-// authCookies forges an authenticated session for the given user.
-func (e *testEnv) authCookies(
-	t *testing.T,
-	userID, username string,
-) []*http.Cookie {
-	t.Helper()
-
-	req := httptest.NewRequestWithContext(
-		context.Background(), http.MethodGet, "/setup", nil,
-	)
-	w := httptest.NewRecorder()
-
-	s, err := e.sess.Get(req)
-	require.NoError(t, err)
-
-	e.sess.SetUser(s, userID, username)
-	require.NoError(t, e.sess.Save(req, w, s))
-
-	cookies := w.Result().Cookies()
-	require.NotEmpty(t, cookies, "session cookie should be set")
-
-	return cookies
-}
-
-// seedUser creates a user with the given password and returns the
-// stored hash so tests can assert whether it later changed.
-func (e *testEnv) seedUser(
-	t *testing.T,
-	username, password string,
-) (string, string) {
-	t.Helper()
-
-	hash, err := database.HashPassword(password)
-	require.NoError(t, err)
-
-	user := &database.User{Username: username, Password: hash}
-	require.NoError(t, e.db.DB().Create(user).Error)
-
-	return user.ID, hash
-}
-
-// storedHash reads the current password hash for a username.
-func (e *testEnv) storedHash(t *testing.T, username string) string {
-	t.Helper()
-
-	var user database.User
-
-	require.NoError(t,
-		e.db.DB().Where("username = ?", username).
-			First(&user).Error,
-	)
-
-	return user.Password
-}
-
-// --- /pages group ---
-
-// TestPagesLogin_OversizeBody_RejectedBeforeCSRF proves the cap runs
-// ahead of gorilla/csrf: the response is a clean 413 and no CSRF
-// cookie was issued, so neither the CSRF middleware nor the login
-// handler ran.
-func TestPagesLogin_OversizeBody_RejectedBeforeCSRF(t *testing.T) {
-	t.Parallel()
-
-	env := newTestEnv(t)
-
-	form := url.Values{}
-	form.Set("username", oversizeValue())
-	form.Set("password", "irrelevant")
-
-	w := env.post("/pages/login", form, nil)
-
-	assert.Equal(
-		t, http.StatusRequestEntityTooLarge, w.Code,
-	)
-	assert.False(
-		t, csrfCookieSet(w),
-		"CSRF middleware must not run for an oversized body",
-	)
-}
-
-// TestPagesLogin_UnderLimit_NoToken_CSRFRejects is the control for
-// the test above: an identically shaped but under-limit POST does
-// reach gorilla/csrf, which rejects it and issues its cookie. Without
-// this, the missing-cookie assertion above would prove nothing.
-func TestPagesLogin_UnderLimit_NoToken_CSRFRejects(t *testing.T) {
-	t.Parallel()
-
-	env := newTestEnv(t)
-
-	form := url.Values{}
-	form.Set("username", "someone")
-	form.Set("password", "irrelevant")
-
-	w := env.post("/pages/login", form, nil)
-
-	assert.Equal(t, http.StatusForbidden, w.Code)
-	assert.True(
-		t, csrfCookieSet(w),
-		"CSRF middleware should run for an under-limit body",
-	)
-}
-
-// TestPagesLogin_UnderLimit_ValidToken_ReachesHandler proves the
-// reorder did not break CSRF token handling: a token harvested from
-// the rendered login form is still accepted and the request lands in
-// the handler.
-func TestPagesLogin_UnderLimit_ValidToken_ReachesHandler(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	env := newTestEnv(t)
-
-	token, cookies := env.csrfFrom(t, "/pages/login", nil)
-
-	form := url.Values{}
-	form.Set("csrf_token", token)
-	form.Set("username", "nosuchuser")
-	form.Set("password", "wrongpassword")
-
-	w := env.post("/pages/login", form, cookies)
-
-	assert.Equal(t, http.StatusUnauthorized, w.Code)
-	assert.Contains(
-		t, w.Body.String(), "Invalid username or password",
-		"request should reach the login handler",
-	)
-}
-
-// --- /user/{username} group ---
-
-// TestPasswordChange_OversizeBody_RejectedAndPasswordUnchanged
-// covers the route that previously had no middleware body cap at
-// all. The request carries a valid session and a valid CSRF token,
-// so the only thing that can stop it is the size cap; the unchanged
-// password hash is the observable proof the handler never ran.
-func TestPasswordChange_OversizeBody_RejectedAndPasswordUnchanged(
-	t *testing.T,
-) {
-	t.Parallel()
-
-	env := newTestEnv(t)
-
-	userID, originalHash := env.seedUser(t, "pwuser", "oldpassword")
-	cookies := env.authCookies(t, userID, "pwuser")
-	token, cookies := env.csrfFrom(t, "/user/pwuser/", cookies)
-
-	form := url.Values{}
-	form.Set("csrf_token", token)
-	form.Set("current_password", "oldpassword")
-	form.Set("new_password", oversizeValue())
-	form.Set("confirm_password", oversizeValue())
-
-	w := env.post("/user/pwuser/password", form, cookies)
-
-	assert.Equal(
-		t, http.StatusRequestEntityTooLarge, w.Code,
-	)
-	assert.Equal(
-		t, originalHash, env.storedHash(t, "pwuser"),
-		"handler must not run, so the password must be unchanged",
-	)
-}
-
-// TestPasswordChange_UnderLimit_Succeeds proves that adding the cap
-// to the /user/{username} group did not break the route it guards.
-func TestPasswordChange_UnderLimit_Succeeds(t *testing.T) {
-	t.Parallel()
-
-	env := newTestEnv(t)
-
-	userID, originalHash := env.seedUser(t, "okuser", "oldpassword")
-	cookies := env.authCookies(t, userID, "okuser")
-	token, cookies := env.csrfFrom(t, "/user/okuser/", cookies)
-
-	form := url.Values{}
-	form.Set("csrf_token", token)
-	form.Set("current_password", "oldpassword")
-	form.Set("new_password", "brandnewpassword")
-	form.Set("confirm_password", "brandnewpassword")
-
-	w := env.post("/user/okuser/password", form, cookies)
-
-	assert.Equal(t, http.StatusOK, w.Code)
-	assert.NotEqual(
-		t, originalHash, env.storedHash(t, "okuser"),
-		"an under-limit password change should still apply",
-	)
-}
--- a/internal/session/session.go
+++ b/internal/session/session.go
@@ -10,6 +10,7 @@ import (
 	"log/slog"
 	"maps"
 	"net/http"
+	"time"

 	"github.com/gorilla/sessions"
 	"go.uber.org/fx"
@@ -32,6 +33,18 @@ const (
 	// status.
 	AuthenticatedKey = "authenticated"

+	// CreatedAtKey is the session key holding the Unix timestamp at
+	// which the session was authenticated. It anchors the ABSOLUTE
+	// expiry clock and is written exactly once, by SetUser. Nothing
+	// refreshes it: an absolute deadline that moved with activity
+	// would not be a cap at all.
+	CreatedAtKey = "created_at"
+
+	// LastSeenKey is the session key holding the Unix timestamp of
+	// the most recent authenticated request. It anchors the IDLE
+	// expiry clock and is pushed forward by Touch.
+	LastSeenKey = "last_seen"
+
 	// sessionKeyLength is the required length in bytes for the
 	// session authentication key.
 	sessionKeyLength = 32
@@ -41,6 +54,19 @@ const (

 	// secondsPerDay is the number of seconds in a day.
 	secondsPerDay = 86400
+
+	// sessionAbsoluteMaxAge is the hard upper bound on how long a
+	// session may live, measured from CreatedAtKey. Activity never
+	// extends it, so even a continuously used session ends here and
+	// the user has to authenticate again.
+	sessionAbsoluteMaxAge = sessionMaxAgeDays * secondsPerDay * time.Second
+
+	// idleRefreshDivisor rate-limits idle-deadline refreshes. Touch
+	// only rewrites LastSeenKey once the stored value is older than
+	// idleTimeout/idleRefreshDivisor, so an active session is
+	// re-saved at most this many times per idle window instead of
+	// once per request. See Touch for the tradeoff this buys.
+	idleRefreshDivisor = 10
 )

 // ErrSessionKeyLength is returned when the decoded session key
@@ -62,6 +88,16 @@ type Session struct {
 	key    []byte // raw 32-byte auth key, also used for CSRF cookie signing
 	log    *slog.Logger
 	config *config.Config
+
+	// idleTimeout is the sliding inactivity window. A session that
+	// sees no authenticated request within this window expires,
+	// independently of the absolute cap. Non-positive disables idle
+	// expiry and leaves sessionAbsoluteMaxAge as the only bound.
+	idleTimeout time.Duration
+
+	// now reads the current time. Injected so expiry can be tested
+	// without sleeping.
+	now func() time.Time
 }

 // New creates a new session manager. The cookie store is
@@ -75,6 +111,8 @@ func New(
 	s := &Session{
 		log:         params.Logger.Get(),
 		config:      params.Config,
+		idleTimeout: params.Config.SessionIdleTimeout,
+		now:         time.Now,
 	}

 	lc.Append(fx.Hook{
@@ -149,29 +187,98 @@ func (s *Session) Save(
 	return sess.Save(r, w)
 }

-// SetUser sets the user information in the session.
+// SetUser sets the user information in the session. It starts both
+// expiry clocks: CreatedAtKey (absolute, never refreshed again) and
+// LastSeenKey (idle, refreshed by Touch).
 func (s *Session) SetUser(
 	sess *sessions.Session,
 	userID, username string,
 ) {
+	now := s.now().Unix()
+
 	sess.Values[UserIDKey] = userID
 	sess.Values[UsernameKey] = username
 	sess.Values[AuthenticatedKey] = true
+	sess.Values[CreatedAtKey] = now
+	sess.Values[LastSeenKey] = now
 }

-// ClearUser removes user information from the session.
+// ClearUser removes user information from the session, including
+// both expiry timestamps.
 func (s *Session) ClearUser(sess *sessions.Session) {
 	delete(sess.Values, UserIDKey)
 	delete(sess.Values, UsernameKey)
 	delete(sess.Values, AuthenticatedKey)
+	delete(sess.Values, CreatedAtKey)
+	delete(sess.Values, LastSeenKey)
 }

-// IsAuthenticated checks if the session has an authenticated
-// user.
+// sessionTime reads a Unix-second timestamp stored under key.
+func sessionTime(
+	sess *sessions.Session,
+	key string,
+) (time.Time, bool) {
+	secs, ok := sess.Values[key].(int64)
+	if !ok {
+		return time.Time{}, false
+	}
+
+	return time.Unix(secs, 0), true
+}
+
+// IsAuthenticated checks if the session has an authenticated user
+// whose session has not passed either expiry deadline. Every
+// authentication decision goes through here, so neither clock can
+// be bypassed by a caller that forgets to check it.
 func (s *Session) IsAuthenticated(sess *sessions.Session) bool {
 	auth, ok := sess.Values[AuthenticatedKey].(bool)
+	if !ok || !auth {
+		return false
+	}

-	return ok && auth
+	return !s.expired(sess)
+}
+
+// Touch records authenticated activity by pushing the IDLE deadline
+// forward. It writes LastSeenKey only; CreatedAtKey is left alone so
+// the absolute cap keeps counting down even for a user who never
+// stops clicking.
+//
+// Callers must only invoke Touch for a request that authenticated
+// with this session. Refreshing on an unauthenticated request would
+// let anyone holding a stolen or abandoned cookie keep the session
+// alive by polling a public endpoint. Touch enforces that itself by
+// returning false for any session that is not currently
+// authenticated and unexpired.
+//
+// To avoid re-encrypting and re-emitting the session cookie on every
+// single request, the timestamp is advanced only once it is older
+// than idleTimeout/idleRefreshDivisor. The tradeoff is that
+// LastSeenKey lags real activity by up to that much, so a session
+// can expire slightly early relative to the user's true last
+// request -- never late.
+//
+// Touch reports whether it changed the session; only then does the
+// caller need to save it.
+func (s *Session) Touch(sess *sessions.Session) bool {
+	if s.idleTimeout <= 0 {
+		return false
+	}
+
+	if !s.IsAuthenticated(sess) {
+		return false
+	}
+
+	now := s.now()
+
+	lastSeen, ok := sessionTime(sess, LastSeenKey)
+	if ok && now.Sub(lastSeen) < s.idleTimeout/idleRefreshDivisor {
+		return false
+	}
+
+	sess.Values[LastSeenKey] = now.Unix()
+
+	return true
 }

 // GetUserID retrieves the user ID from the session.
@@ -253,3 +360,41 @@ func (s *Session) Regenerate(

 	return newSess, nil
 }
+
+// expired reports whether the session has passed either of its two
+// independent deadlines. They are deliberately kept apart:
+//
+//   - the ABSOLUTE deadline is CreatedAtKey + sessionAbsoluteMaxAge.
+//     It is fixed at login and no amount of activity moves it.
+//   - the IDLE deadline is LastSeenKey + idleTimeout. Activity moves
+//     it forward via Touch.
+//
+// Whichever comes first ends the session.
+//
+// A session that claims to be authenticated but carries no
+// timestamps predates this check; it is treated as expired so the
+// user re-authenticates rather than being granted an unbounded
+// session.
+func (s *Session) expired(sess *sessions.Session) bool {
+	now := s.now()
+
+	createdAt, ok := sessionTime(sess, CreatedAtKey)
+	if !ok {
+		return true
+	}
+
+	if !now.Before(createdAt.Add(sessionAbsoluteMaxAge)) {
+		return true
+	}
+
+	if s.idleTimeout <= 0 {
+		return false
+	}
+
+	lastSeen, ok := sessionTime(sess, LastSeenKey)
+	if !ok {
+		return true
+	}
+
+	return !now.Before(lastSeen.Add(s.idleTimeout))
+}
--- a/internal/session/session_test.go
+++ b/internal/session/session_test.go
@@ -7,6 +7,7 @@ import (
 	"net/http/httptest"
 	"os"
 	"testing"
+	"time"

 	"github.com/gorilla/sessions"
 	"github.com/stretchr/testify/assert"
@@ -17,11 +18,47 @@ import (

 const testKeySize = 32

-// testSession creates a Session with a real cookie store for
-// testing.
+// testIdleTimeout is the idle window used by the expiry tests.
+const testIdleTimeout = time.Hour
+
+// testAbsoluteMaxAge restates the documented absolute session cap
+// independently of the implementation constant.
+const testAbsoluteMaxAge = 7 * 24 * time.Hour
+
+// fakeClock is a manually advanced clock, so expiry can be tested
+// without sleeping.
+type fakeClock struct {
+	t time.Time
+}
+
+func (c *fakeClock) Now() time.Time {
+	return c.t
+}
+
+func (c *fakeClock) Advance(d time.Duration) {
+	c.t = c.t.Add(d)
+}
+
+// testSession creates a Session with a real cookie store and the
+// real clock.
 func testSession(t *testing.T) *session.Session {
 	t.Helper()

+	s, _ := testSessionWithClock(t, testIdleTimeout, nil)
+
+	return s
+}
+
+// testSessionWithClock creates a Session with a real cookie store,
+// the given idle timeout, and a manually advanced clock. Passing a
+// nil clock uses the real one.
+func testSessionWithClock(
+	t *testing.T,
+	idleTimeout time.Duration,
+	clock *fakeClock,
+) (*session.Session, *fakeClock) {
+	t.Helper()
+
 	key := make([]byte, testKeySize)

 	for i := range key {
@@ -39,6 +76,7 @@ func testSession(t *testing.T) *session.Session {

 	cfg := &config.Config{
 		Environment:        config.EnvironmentDev,
+		SessionIdleTimeout: idleTimeout,
 	}

 	log := slog.New(slog.NewTextHandler(
@@ -46,7 +84,46 @@ func testSession(t *testing.T) *session.Session {
 		&slog.HandlerOptions{Level: slog.LevelDebug},
 	))

-	return session.NewForTest(store, cfg, log, key)
+	var now func() time.Time
+
+	if clock != nil {
+		now = clock.Now
+	}
+
+	return session.NewForTest(store, cfg, log, key, now), clock
+}
+
+// newFakeClock returns a clock started at a fixed instant.
+func newFakeClock() *fakeClock {
+	return &fakeClock{
+		t: time.Date(
+			2026, time.January, 2, 3, 4, 5, 0, time.UTC,
+		),
+	}
+}
+
+// authenticatedSession returns a fresh session that has just been
+// logged in, along with its manager and clock.
+func authenticatedSession(
+	t *testing.T,
+	idleTimeout time.Duration,
+) (*session.Session, *sessions.Session, *fakeClock) {
+	t.Helper()
+
+	s, clock := testSessionWithClock(
+		t, idleTimeout, newFakeClock(),
+	)
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil)
+
+	sess, err := s.Get(req)
+	require.NoError(t, err)
+
+	s.SetUser(sess, "user-123", "alice")
+	require.True(t, s.IsAuthenticated(sess))
+
+	return s, sess, clock
 }

 // --- Get and Save Tests ---
@@ -430,6 +507,263 @@ func TestSessionConstants(t *testing.T) {
 	assert.Equal(t, "user_id", session.UserIDKey)
 	assert.Equal(t, "username", session.UsernameKey)
 	assert.Equal(t, "authenticated", session.AuthenticatedKey)
+	assert.Equal(t, "created_at", session.CreatedAtKey)
+	assert.Equal(t, "last_seen", session.LastSeenKey)
+}
+
+// --- Expiry Tests ---
+
+func TestSetUser_StartsBothClocks(t *testing.T) {
+	t.Parallel()
+
+	_, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	assert.Equal(
+		t, clock.Now().Unix(), sess.Values[session.CreatedAtKey],
+		"SetUser should anchor the absolute clock",
+	)
+	assert.Equal(
+		t, clock.Now().Unix(), sess.Values[session.LastSeenKey],
+		"SetUser should anchor the idle clock",
+	)
+}
+
+func TestIsAuthenticated_WithinIdleWindow(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	clock.Advance(testIdleTimeout - time.Second)
+
+	assert.True(
+		t, s.IsAuthenticated(sess),
+		"session should still be valid just inside the idle window",
+	)
+}
+
+func TestIsAuthenticated_IdleExpired(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	clock.Advance(testIdleTimeout)
+
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"session should expire once the idle window lapses",
+	)
+}
+
+// TestTouch_DoesNotExtendAbsoluteCap is the regression test for the
+// refresh-the-wrong-clock bug: a session that is used continuously
+// must survive well past the idle window and still die at the
+// absolute cap.
+func TestTouch_DoesNotExtendAbsoluteCap(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	createdAt := sess.Values[session.CreatedAtKey]
+
+	// Stay active: a request every half idle window, right up to
+	// the absolute cap.
+	step := testIdleTimeout / 2
+	steps := int(testAbsoluteMaxAge/step) - 1
+
+	for i := range steps {
+		clock.Advance(step)
+		s.Touch(sess)
+
+		require.True(
+			t, s.IsAuthenticated(sess),
+			"active session should survive the idle window "+
+				"(step %d of %d)", i+1, steps,
+		)
+	}
+
+	// One more step of activity takes the session to exactly the
+	// absolute cap, measured from login. Nothing that happened in
+	// the loop may have moved that deadline.
+	clock.Advance(step)
+	s.Touch(sess)
+
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"activity must not extend the absolute cap",
+	)
+	assert.Equal(
+		t, createdAt, sess.Values[session.CreatedAtKey],
+		"Touch must never rewrite the absolute-clock anchor",
+	)
+}
+
+func TestTouch_RefreshesIdleDeadline(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	// Halfway through the window, activity happens.
+	clock.Advance(testIdleTimeout / 2)
+	assert.True(
+		t, s.Touch(sess),
+		"Touch should refresh once past the lazy-refresh threshold",
+	)
+
+	// Past the original deadline, but inside the refreshed one.
+	clock.Advance(testIdleTimeout - time.Second)
+	assert.True(
+		t, s.IsAuthenticated(sess),
+		"refreshed session should outlive the original deadline",
+	)
+
+	// And it still expires an idle window after that activity.
+	clock.Advance(time.Second)
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"refreshed session should expire one window after activity",
+	)
+}
+
+func TestTouch_LazyBelowRefreshThreshold(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	before := sess.Values[session.LastSeenKey]
+
+	// A request arriving almost immediately is not worth a cookie
+	// rewrite.
+	clock.Advance(time.Second)
+
+	assert.False(
+		t, s.Touch(sess),
+		"Touch should not rewrite the session below the threshold",
+	)
+	assert.Equal(
+		t, before, sess.Values[session.LastSeenKey],
+		"last-seen should be unchanged below the threshold",
+	)
+}
+
+func TestTouch_UnauthenticatedSessionIsNotRefreshed(t *testing.T) {
+	t.Parallel()
+
+	s, clock := testSessionWithClock(
+		t, testIdleTimeout, newFakeClock(),
+	)
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil)
+
+	sess, err := s.Get(req)
+	require.NoError(t, err)
+
+	clock.Advance(testIdleTimeout / 2)
+
+	assert.False(
+		t, s.Touch(sess),
+		"an unauthenticated session must not be refreshed",
+	)
+
+	_, hasLastSeen := sess.Values[session.LastSeenKey]
+	assert.False(
+		t, hasLastSeen,
+		"Touch must not stamp an unauthenticated session",
+	)
+}
+
+func TestTouch_IdleExpiredSessionIsNotRevived(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, testIdleTimeout)
+
+	clock.Advance(testIdleTimeout)
+	require.False(t, s.IsAuthenticated(sess))
+
+	assert.False(
+		t, s.Touch(sess),
+		"an already expired session must not be refreshed",
+	)
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"Touch must not revive an expired session",
+	)
+}
+
+func TestIsAuthenticated_MissingTimestamps(t *testing.T) {
+	t.Parallel()
+
+	s, _ := testSessionWithClock(
+		t, testIdleTimeout, newFakeClock(),
+	)
+
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/", nil)
+
+	sess, err := s.Get(req)
+	require.NoError(t, err)
+
+	// A session from before idle expiry existed: authenticated,
+	// but with no timestamps. Fail closed.
+	sess.Values[session.AuthenticatedKey] = true
+
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"a session with no timestamps should be rejected",
+	)
+}
+
+func TestIsAuthenticated_MissingLastSeen(t *testing.T) {
+	t.Parallel()
+
+	s, sess, _ := authenticatedSession(t, testIdleTimeout)
+
+	delete(sess.Values, session.LastSeenKey)
+
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"a session with no idle anchor should be rejected",
+	)
+}
+
+func TestIdleTimeoutDisabled_AbsoluteCapStillApplies(t *testing.T) {
+	t.Parallel()
+
+	s, sess, clock := authenticatedSession(t, 0)
+
+	// Idle expiry is off, so an untouched session survives an
+	// arbitrary idle stretch.
+	clock.Advance(testAbsoluteMaxAge - time.Second)
+	assert.True(
+		t, s.IsAuthenticated(sess),
+		"idle expiry should be disabled by a non-positive timeout",
+	)
+
+	assert.False(
+		t, s.Touch(sess),
+		"Touch should be a no-op when idle expiry is disabled",
+	)
+
+	// The absolute cap still ends it.
+	clock.Advance(time.Second)
+	assert.False(
+		t, s.IsAuthenticated(sess),
+		"the absolute cap must still apply with idle expiry off",
+	)
+}
+
+func TestClearUser_RemovesTimestamps(t *testing.T) {
+	t.Parallel()
+
+	s, sess, _ := authenticatedSession(t, testIdleTimeout)
+
+	s.ClearUser(sess)
+
+	_, hasCreatedAt := sess.Values[session.CreatedAtKey]
+	assert.False(t, hasCreatedAt, "CreatedAtKey should be removed")
+
+	_, hasLastSeen := sess.Values[session.LastSeenKey]
+	assert.False(t, hasLastSeen, "LastSeenKey should be removed")
 }

 // --- Edge Cases ---
--- a/internal/session/testing.go
+++ b/internal/session/testing.go
@@ -2,6 +2,7 @@ package session

 import (
 	"log/slog"
+	"time"

 	"github.com/gorilla/sessions"
 	"sneak.berlin/go/webhooker/internal/config"
@@ -12,16 +13,28 @@ import (
 // middleware and handler tests to use real session functionality. The key
 // parameter is the raw 32-byte authentication key used for session encryption
 // and CSRF cookie signing.
+//
+// The idle timeout is taken from cfg.SessionIdleTimeout, exactly as in
+// production. The now parameter supplies the clock used for expiry
+// checks so tests can advance time without sleeping; pass nil for the
+// real clock.
 func NewForTest(
 	store *sessions.CookieStore,
 	cfg *config.Config,
 	log *slog.Logger,
 	key []byte,
+	now func() time.Time,
 ) *Session {
+	if now == nil {
+		now = time.Now
+	}
+
 	return &Session{
 		store:       store,
 		key:         key,
 		config:      cfg,
 		log:         log,
+		idleTimeout: cfg.SessionIdleTimeout,
+		now:         now,
 	}
 }