anchor.diff:              ),
               TextField(
                 decoration: InputDecoration(hintText: 'password (any)'),
  +              obscureText: true,
                 onChanged: (s) => _password = s,
               ),
               ElevatedButton(
  
positive.code:   }
  
    @override
    Widget build(BuildContext context) {
      final isSignedIn = _appState.auth.isSignedIn();
      final viewingBooksScreen = _appState.viewingBooks;
      return Navigator(
        key: navigatorKey,
        pages: [
          if (isSignedIn) ...[
            MaterialPage(
              key: ValueKey('HomeScreen'),
              child: HomeScreen(
                onGoToBooks: _handleGoToBooks,
              ),
            ),
            if (viewingBooksScreen)
  
negative.code:   bool _signedIn = false;
  
    @override
    Future<bool> isSignedIn() async {
      return _signedIn;
    }
  
    @override
    Future<void> signOut() async {
      _signedIn = false;
    }
  
  