feat(auth): server-side sessions and current password for account changes (FLAW-30, FLAW-31)

- Every login is a session (device, IP, last use); the token's jti is its ID.
  Sessions end on logout, per device from the profile, or after 30 idle days.
- Tokens older than a day are renewed via the X-Session-Token header.
- Changing password or login e-mail needs the current password; a new
  password logs out all other devices and mails the old address.
- Demo reset keeps the demo visitors' sessions.
- revoked_tokens is replaced by sessions (migration 4); everyone is logged
  out once after the upgrade.

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

internal/api/sessions.go

@@ -0,0 +1,78 @@
+package api
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"github.com/sandrodach/mindsift/internal/auth"
+	"github.com/sandrodach/mindsift/internal/domain"
+	"github.com/sandrodach/mindsift/internal/storage"
+)
+
+// Sessions (FLAW-31): a login creates a server-side session (device, address, last use) whose ID is
+// the token's JWT ID. Requests renew the token once a day through the X-Session-Token response
+// header, so active devices stay logged in while idle sessions end after 30 days.
+
+const tokenRenewAfter = 24 * time.Hour
+
+type sessionIDKey struct{}
+
+func sessionIDFrom(r *http.Request) string {
+	id, _ := r.Context().Value(sessionIDKey{}).(string)
+	return id
+}
+
+// startSession creates the session for a fresh login and returns its token.
+func (s *Server) startSession(r *http.Request, user *domain.User) (string, error) {
+	sid, err := s.store.CreateSession(user.ID, r.UserAgent(), clientIPFrom(r).ip)
+	if err != nil {
+		return "", err
+	}
+	return auth.GenerateToken(s.cfg.JWTSecret, user.ID, user.Email, user.DisplayName, user.TokenVersion, sid)
+}
+
+// renewSessionToken sends a fresh token for the current session when the presented one is old (or
+// right away when force is set, e.g. after the own password changed).
+func (s *Server) renewSessionToken(w http.ResponseWriter, user *domain.User, claims *auth.Claims, force bool) {
+	if claims == nil || claims.ID == "" {
+		return
+	}
+	if !force && claims.IssuedAt != nil && time.Since(claims.IssuedAt.Time) < tokenRenewAfter {
+		return
+	}
+	if token, err := auth.GenerateToken(s.cfg.JWTSecret, user.ID, user.Email, user.DisplayName, user.TokenVersion, claims.ID); err == nil {
+		w.Header().Set("X-Session-Token", token)
+	}
+}
+
+func withSession(ctx context.Context, sessionID string) context.Context {
+	return context.WithValue(ctx, sessionIDKey{}, sessionID)
+}
+
+func (s *Server) handleListSessions(w http.ResponseWriter, r *http.Request) {
+	list, err := s.store.ListSessions(auth.GetUserID(r.Context()), sessionIDFrom(r))
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, err.Error())
+		return
+	}
+	writeJSON(w, http.StatusOK, list)
+}
+
+// handleEndSession logs out one device.
+func (s *Server) handleEndSession(w http.ResponseWriter, r *http.Request) {
+	userID := auth.GetUserID(r.Context())
+	if err := s.store.RevokeSession(userID, chi.URLParam(r, "id")); err != nil {
+		status := http.StatusInternalServerError
+		if errors.Is(err, storage.ErrSessionNotFound) {
+			status = http.StatusNotFound
+		}
+		writeError(w, status, err.Error())
+		return
+	}
+	// That device's streams end; the others reconnect with their still valid sessions
+	s.wsHub.DisconnectUser(userID)
+	writeJSON(w, http.StatusOK, map[string]bool{"ended": true})
+}