fix(auth): stateless session cookie — stop logging users out on deploy (ADR-029)

Pilot feedback: lots of re-logging-in on iPhone. Three causes: sessions lived in
an in-memory map (wiped on every pod restart/deploy), a 1h TTL (idle >1h forced
re-login on a check-back-tomorrow reader), and a session cookie with no Max-Age
(dropped on Safari close). Each re-login is the full IdP redirect dance.

Make sessions stateless: identity + absolute expiry live inside the existing
HMAC-signed cookie (no server table), TTL 1h → 30 days sliding, cookie now
persistent (Max-Age). Survives restarts (test: a cookie from one instance is
accepted by a fresh instance with the same secret), browser-close, and idle.
Trade: no server-side revocation — logout clears the cookie client-side; rotating
tapir-session-secret is the global logout lever. Accepted for the Stage-0 reader.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

DECISIONS.md

@@ -1128,6 +1128,40 @@ Spec: `docs/specs/onboarding-wow-burst.md`.
 
 ---
 
+## ADR-029 — Stateless session cookie (survives restarts, browser-close, idle)
+
+**Status:** Accepted (2026-06-11). Triggered by pilot feedback: "lots of clicking to log in again
+on iPhone." Supersedes the in-memory session store in the ADR-011 login.
+
+**Context.** Three compounding causes made users re-login constantly:
+1. **In-memory session store** (`sessionStore` map) — wiped on every pod restart, so each deploy
+   logged everyone out. During the active build period that was ~15 logouts.
+2. **1-hour session TTL** — for a "check back tomorrow" reader, idle > 1h forced a re-login on
+   nearly every visit.
+3. **No cookie Max-Age** — a session cookie (deleted on browser/app close); iPhone Safari closing
+   the tab dropped it.
+Each re-login is the full Dex/Authentik redirect dance — many taps on mobile.
+
+**Decision.** Make the session **stateless**: the identity (subject + email) and an absolute
+expiry live INSIDE the existing HMAC-signed (HS256) cookie — no server-side table. Plus:
+- **30-day sliding TTL** (was 1h), re-signed on each request so an active user never lapses.
+- **Persistent cookie** (`Max-Age` set) so it survives browser/app close.
+The cookie is HttpOnly + Secure + SameSite=Lax; the HMAC (keyed by the stable ESO
+`tapir-session-secret`, which does NOT rotate per deploy) makes it tamper-proof. The payload is
+identity, not secrets — the OIDC access/ID tokens are still discarded after callback.
+
+**Consequences.** A deploy/restart no longer logs anyone out (proven by a test: a cookie issued by
+one instance is accepted by a fresh instance with the same secret); works across replicas for
+free. **Trade:** no server-side revocation — `logout` clears the cookie client-side, but a copied
+cookie stays valid until expiry. Accepted for the Stage-0 reader pilot; revisit (server-side
+revocation list, or shorter TTL + refresh) if it ever holds sensitive actions. Rotating
+`tapir-session-secret` invalidates all sessions — the global logout lever.
+
+**Not addressed here:** the tap-count of the IdP login page itself is Authentik's UX; with
+re-login now rare (30-day idle or explicit logout), it matters far less.
+
+---
+
 ## Rejected alternatives
 
 Approaches considered during the 2026-06-02 planning + grill session and **deliberately not

internal/web/oidc/oidc.go

@@ -7,10 +7,11 @@
 // Authentication is real (Dex OIDC) and is the only gate: any Dex-authenticated
 // subject may sign in (ADR-012 dropped ADR-011's single-subject allowlist).
 // Authorization/registration is layered on top in internal/web (an authenticated
-// subject with no tapir user is routed to registration). Sessions are server-side
-// (in-memory, fine for the single Stage-1 replica) addressed by an HMAC-signed
-// (HS256) HttpOnly Secure SameSite=Lax cookie with a short TTL and sliding
-// refresh. Tokens are never logged.
+// subject with no tapir user is routed to registration). Sessions are STATELESS
+// (ADR-029): the identity + expiry live inside an HMAC-signed (HS256) HttpOnly
+// Secure SameSite=Lax persistent cookie with a long sliding TTL — no server-side
+// table, so a deploy/restart never logs anyone out and the cookie also survives
+// browser-close. Tokens are never logged; logout clears the cookie client-side.
 //
 // This is mcp-chassis's cousin but NOT the same code: mcp-chassis validates
 // inbound Bearer JWTs for MCP APIs; this is a browser session login.
@@ -47,7 +48,11 @@ type Config struct {
 }
 
 const (
-	defaultSessionTTL = time.Hour
+	// defaultSessionTTL is generous and sliding: Tapir is a "check back tomorrow"
+	// reader, so a short TTL meant a re-login (full IdP redirect dance) on almost
+	// every visit. 30 days, slid forward on each request, keeps a regular user
+	// logged in indefinitely while an abandoned session still lapses.
+	defaultSessionTTL = 30 * 24 * time.Hour
 	pendingTTL        = 10 * time.Minute
 	sessionCookie     = "tapir_session"
 	loginPath         = "/auth/login"
@@ -59,7 +64,6 @@ type DexAuth struct {
 	oauth    *oauth2.Config
 	verifier *oidc.IDTokenVerifier
 
-	sessions   *sessionStore
 	pending    *pendingStore
 	secret     []byte
 	sessionTTL time.Duration
@@ -127,7 +131,6 @@ func New(ctx context.Context, cfg Config, opts ...Option) (*DexAuth, error) {
 			RedirectURL:  cfg.RedirectURL,
 			Scopes:       []string{oidc.ScopeOpenID, "profile", "email"},
 		},
-		sessions:   newSessionStore(),
 		pending:    newPendingStore(),
 		secret:     []byte(cfg.SessionSecret),
 		sessionTTL: defaultSessionTTL,
@@ -159,31 +162,31 @@ func (d *DexAuth) Middleware(h http.Handler) http.Handler {
 			h.ServeHTTP(w, r)
 			return
 		}
-		sid, ok := d.sessionID(r)
+		c, err := r.Cookie(sessionCookie)
+		if err != nil {
+			d.redirectUnauthenticated(w, r)
+			return
+		}
+		user, _, ok := d.decodeSession(c.Value, d.now())
 		if !ok {
 			d.redirectUnauthenticated(w, r)
 			return
 		}
-		if _, ok := d.sessions.get(sid, d.now()); !ok {
-			d.redirectUnauthenticated(w, r)
-			return
-		}
-		d.sessions.refresh(sid, d.now().Add(d.sessionTTL)) // sliding refresh
+		// Sliding refresh: re-issue the cookie with a fresh expiry so an active
+		// user never lapses (the expiry lives in the cookie, so sliding = re-sign).
+		d.setSessionCookie(w, d.encodeSession(user, d.now().Add(d.sessionTTL)))
 		h.ServeHTTP(w, r)
 	})
 }
 
-// CurrentUser resolves the authenticated principal from the session cookie.
+// CurrentUser resolves the authenticated principal from the stateless cookie.
 func (d *DexAuth) CurrentUser(r *http.Request) (web.User, bool) {
-	sid, ok := d.sessionID(r)
-	if !ok {
+	c, err := r.Cookie(sessionCookie)
+	if err != nil {
 		return web.User{}, false
 	}
-	data, ok := d.sessions.get(sid, d.now())
-	if !ok {
-		return web.User{}, false
-	}
-	return data.user, true
+	user, _, ok := d.decodeSession(c.Value, d.now())
+	return user, ok
 }
 
 func (d *DexAuth) handleLogin(w http.ResponseWriter, r *http.Request) {
@@ -248,23 +251,15 @@ func (d *DexAuth) handleCallback(w http.ResponseWriter, r *http.Request) {
 	}
 	_ = idToken.Claims(&claims) // email is best-effort; subject is the identity
 
-	sid, err := randToken()
-	if err != nil {
-		http.Error(w, "internal error", http.StatusInternalServerError)
-		return
-	}
-	d.sessions.put(sid, sessionData{
-		user:   web.User{Subject: idToken.Subject, Email: claims.Email},
-		expiry: d.now().Add(d.sessionTTL),
-	})
-	d.setSessionCookie(w, sid)
+	user := web.User{Subject: idToken.Subject, Email: claims.Email}
+	d.setSessionCookie(w, d.encodeSession(user, d.now().Add(d.sessionTTL)))
 	http.Redirect(w, r, "/", http.StatusFound)
 }
 
 func (d *DexAuth) handleLogout(w http.ResponseWriter, r *http.Request) {
-	if sid, ok := d.sessionID(r); ok {
-		d.sessions.delete(sid)
-	}
+	// Stateless sessions: clearing the cookie logs the browser out. There is no
+	// server-side record to delete (ADR-029); a copy of the cookie stays valid
+	// until its expiry — an accepted trade for the Stage-0 reader app.
 	d.clearSessionCookie(w)
 	// Land on the public landing page, not the login endpoint: a just-logged-out
 	// visitor should see /welcome, not be bounced straight back into a Dex login.
@@ -287,22 +282,19 @@ func (d *DexAuth) redirectToLogin(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, loginPath, http.StatusFound)
 }
 
-func (d *DexAuth) sessionID(r *http.Request) (string, bool) {
-	c, err := r.Cookie(sessionCookie)
-	if err != nil {
-		return "", false
-	}
-	return d.unsign(c.Value)
-}
-
-func (d *DexAuth) setSessionCookie(w http.ResponseWriter, sid string) {
+// setSessionCookie writes the signed session value as a PERSISTENT cookie
+// (Max-Age set), so it survives the browser/app being closed — a session cookie
+// (no Max-Age) was dropped on iPhone Safari close, forcing re-login. value is the
+// already-signed payload from encodeSession.
+func (d *DexAuth) setSessionCookie(w http.ResponseWriter, value string) {
 	http.SetCookie(w, &http.Cookie{
 		Name:     sessionCookie,
-		Value:    d.sign(sid),
+		Value:    value,
 		Path:     "/",
 		HttpOnly: true,
 		Secure:   !d.insecure,
 		SameSite: http.SameSiteLaxMode,
+		MaxAge:   int(d.sessionTTL.Seconds()),
 	})
 }
 

internal/web/oidc/oidc_test.go

@@ -306,13 +306,42 @@ func TestLogoutClearsSession(t *testing.T) {
 	require.Equal(t, http.StatusFound, rec.Code)
 	require.Equal(t, "/welcome", rec.Header().Get("Location"), "logout lands on the public page")
 	cleared := sessionCookie(t, rec.Result())
-	require.Less(t, cleared.MaxAge, 0, "logout expires the cookie")
+	require.Less(t, cleared.MaxAge, 0, "logout expires the cookie so the browser drops it")
+	require.Empty(t, cleared.Value, "logout blanks the cookie value")
 
-	// The server-side session is gone: the original cookie no longer resolves.
+	// Sessions are stateless (ADR-029): logout clears the cookie client-side, so a
+	// request carrying the cleared (empty) cookie is unauthenticated. The original
+	// signed cookie remains technically valid until its expiry — the accepted
+	// trade for no server-side store; the browser no longer holds it.
 	check := httptest.NewRequest(http.MethodGet, "/", nil)
-	check.AddCookie(cookie)
+	check.AddCookie(cleared)
 	_, ok := auth.CurrentUser(check)
-	require.False(t, ok)
+	require.False(t, ok, "the cleared cookie does not authenticate")
+}
+
+// TestSessionSurvivesRestart is the core of ADR-029: a cookie issued by one
+// process is accepted by a FRESH instance with the same session secret — so a
+// deploy/pod-restart no longer logs users out (the old in-memory store did).
+func TestSessionSurvivesRestart(t *testing.T) {
+	f := newFakeIssuer(t)
+	auth1 := newAuth(t, f)
+	cookie := authenticate(t, auth1, f)
+
+	auth2 := newAuth(t, f) // simulate a redeploy: new process, same SessionSecret
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.AddCookie(cookie)
+	user, ok := auth2.CurrentUser(req)
+	require.True(t, ok, "a session must survive a restart (stateless signed cookie)")
+	require.Equal(t, testSubject, user.Subject)
+}
+
+// TestSessionCookieIsPersistent: the cookie carries a positive Max-Age so it
+// survives the browser/app being closed (a session cookie was dropped on iOS).
+func TestSessionCookieIsPersistent(t *testing.T) {
+	f := newFakeIssuer(t)
+	auth := newAuth(t, f)
+	cookie := authenticate(t, auth, f)
+	require.Greater(t, cookie.MaxAge, 0, "session cookie must be persistent (Max-Age set)")
 }
 
 func TestExpiredSessionRejected(t *testing.T) {

internal/web/oidc/session.go

@@ -6,6 +6,7 @@ import (
 	"crypto/sha256"
 	"encoding/base64"
 	"encoding/hex"
+	"encoding/json"
 	"fmt"
 	"strings"
 	"sync"
@@ -53,56 +54,44 @@ func (d *DexAuth) unsign(signed string) (string, bool) {
 	return value, true
 }
 
-// sessionData is the server-side session record.
-type sessionData struct {
-	user   web.User
-	expiry time.Time
+// sessionClaims is the self-contained session payload carried INSIDE the signed
+// cookie — there is no server-side session table. This is deliberate (ADR-029):
+// an in-memory store was wiped on every pod restart, logging every user out on
+// each deploy, and a stateless cookie also survives browser-close and works
+// across replicas. It holds only the identity (subject + email, not secret) and
+// an absolute expiry; the HMAC tag (sign/unsign) makes it tamper-proof.
+type sessionClaims struct {
+	Sub   string `json:"s"`
+	Email string `json:"e"`
+	Exp   int64  `json:"x"` // unix seconds; absolute expiry
 }
 
-// sessionStore is an in-memory session table. Single replica at Stage 0, so an
-// in-process map is sufficient; it is safe for concurrent use.
-type sessionStore struct {
-	mu sync.Mutex
-	m  map[string]sessionData
+// encodeSession produces the signed cookie value for a user with the given expiry.
+func (d *DexAuth) encodeSession(u web.User, exp time.Time) string {
+	b, _ := json.Marshal(sessionClaims{Sub: u.Subject, Email: u.Email, Exp: exp.Unix()})
+	return d.sign(base64.RawURLEncoding.EncodeToString(b))
 }
 
-func newSessionStore() *sessionStore { return &sessionStore{m: make(map[string]sessionData)} }
-
-func (s *sessionStore) put(id string, d sessionData) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	s.m[id] = d
-}
-
-// get returns the session if present and unexpired; expired entries are evicted.
-func (s *sessionStore) get(id string, now time.Time) (sessionData, bool) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	d, ok := s.m[id]
+// decodeSession verifies the cookie's HMAC, parses the claims, and checks expiry.
+// It returns the user and the absolute expiry on success.
+func (d *DexAuth) decodeSession(cookieValue string, now time.Time) (web.User, time.Time, bool) {
+	payload, ok := d.unsign(cookieValue)
 	if !ok {
-		return sessionData{}, false
+		return web.User{}, time.Time{}, false
 	}
-	if !now.Before(d.expiry) {
-		delete(s.m, id)
-		return sessionData{}, false
+	raw, err := base64.RawURLEncoding.DecodeString(payload)
+	if err != nil {
+		return web.User{}, time.Time{}, false
 	}
-	return d, true
-}
-
-// refresh slides an existing session's expiry forward; a no-op for unknown ids.
-func (s *sessionStore) refresh(id string, expiry time.Time) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	if d, ok := s.m[id]; ok {
-		d.expiry = expiry
-		s.m[id] = d
+	var c sessionClaims
+	if err := json.Unmarshal(raw, &c); err != nil {
+		return web.User{}, time.Time{}, false
 	}
-}
-
-func (s *sessionStore) delete(id string) {
-	s.mu.Lock()
-	defer s.mu.Unlock()
-	delete(s.m, id)
+	exp := time.Unix(c.Exp, 0)
+	if !now.Before(exp) {
+		return web.User{}, time.Time{}, false // expired
+	}
+	return web.User{Subject: c.Sub, Email: c.Email}, exp, true
 }
 
 // pendingData holds the nonce bound to an in-flight authorization request.