Redirect to login (and continue after)

Some routes need a signed-in user. When a logged-out user heads to one, show login instead — and after they sign in, continue to where they were going, not to a generic home screen.

The recipe

Mark protected routes with an interface:

abstract interface class RequiresAuth {}

final class Payment extends AppRoute implements RequiresAuth {
  const Payment();
}

Write a guard that stashes the intended stack and redirects:

List<AppRoute>? _intended;

KaiselGuard<AppRoute> authGuard(ValueListenable<bool> loggedIn) {
  return (current, proposed) {
    final needsAuth = proposed.any((r) => r is RequiresAuth);
    if (needsAuth && !loggedIn.value) {
      _intended = proposed;
      return const [Login()];
    }
    return proposed;
  };
}

Register it: KaiselRouterConfig(guards: [authGuard(_loggedIn)], ...).

After a successful login, replay the stash:

_loggedIn.value = true;
context.router<AppRoute>().set(_intended ?? const [Home()]);
_intended = null;

Why this works so cleanly

The intended destination is plain data — a List<AppRoute> — so the whole stack is reconstructed, not just the final screen: if the user was headed to [Home(), Cart(), Payment()], they land on Payment with Cart beneath it and back behaving correctly. The same guard handles deep links into protected routes with zero extra code.

Notes

• Guards don’t run on system back (the pop has already animated by the time the router hears about it). For “force back to login on logout,” listen to your auth state and call router.set(const [Login()]) directly.
• The guard is a pure function — unit test it with two lists and no widgets. See the guards reference.
• Runnable version: main_auth_redirect.dart.