Encrypt cookies

internal/server/server.go

@@ -37,6 +37,10 @@ type Server struct {
 	// none. Resolved once: the assets cannot change while the process runs.
 	favicon string
 
+	// sessions seals the login cookie, so the token it remembers is not
+	// legible to anyone reading the browser's cookie jar.
+	sessions *sealer
+
 	now func() time.Time // swappable in tests
 }
 
@@ -45,6 +49,10 @@ func New(cfg *config.Config, st *store.Store, tokens *auth.File, log *slog.Logge
 	if err != nil {
 		return nil, err
 	}
+	sessions, err := newSealer(sessionKeyPath(cfg.DataDir))
+	if err != nil {
+		return nil, err
+	}
 	s := &Server{
 		cfg:         cfg,
 		store:       st,
@@ -56,6 +64,7 @@ func New(cfg *config.Config, st *store.Store, tokens *auth.File, log *slog.Logge
 		slots:       make(chan struct{}, cfg.MaxConcurrent),
 		now:         time.Now,
 		favicon:     faviconFor(web.Static()),
+		sessions:    sessions,
 	}
 	s.handler = s.routes()
 	return s, nil
@@ -245,7 +254,7 @@ func (s *Server) page(r *http.Request, title string, script bool) page {
 	if s.favicon != "" {
 		p.Favicon = s.cfg.BasePath + "static/" + s.favicon
 	}
-	if lim, err := s.limitsFor(r, cookieCredential(r)); err == nil {
+	if lim, err := s.limitsFor(r, s.cookieCredential(r)); err == nil {
 		p.User, p.Admin = lim.Name, lim.Admin
 	}
 	return p