sign_in_screen.dart

@override
Widget build(BuildContext context) {
  return AppBackground(
    child: AnimatedSize(
      duration: const Duration(milliseconds: 250),
      (1)
      child: FutureBuilder<AuthSession>(
        (2)
        future: Amplify.Auth.fetchAuthSession(),
        builder: (context, snapshot) {
          (3)
          if (snapshot.hasData) {
            if (snapshot.data!.isSignedIn) {
              context.go('/home');
            }
            // Update the UI on next step
            return const SizedBox.shrink();
          } else {
            (4)
            return const SizedBox(
              height: 100,
              child: Center(
                child: CircularProgressIndicator(),
              ),
            );
          }
        },
      ),
    ),
  );
}