sign_in_screen.dart

Future<void> _loginUser() async {
  // (1) 
  if (_formKey.currentState!.validate()) {
    setState(() {
      _isLoading = true;
      _errorMessage = null;
    });
    try {
      // (2)
      final result = await Amplify.Auth.signIn(
        username: _usernameController.text,
        password: _passwordController.text,
      );
      setState(() {
        _isLoading = false;
      });
      // (3)
      if (result.isSignedIn && mounted) {
        context.go('/home');
      // (4)  
      } else if (result.nextStep?.signInStep == CognitoSignInStep.confirmSignUp.value) {
        context.go(
          '/confirm-user',
          extra: _usernameController.text,
        );
        await Amplify.Auth.resendSignUpCode(
          username: _usernameController.text,
        );
      }
    // (5)  
    } on UserNotFoundException {
      setState(() {
        _isLoading = false;
        _errorMessage = 'The user is not found. Please register';
      });
    // (6)
    } on UserNotConfirmedException {
      setState(() {
        _isLoading = false;
      });
      context.go(
        '/confirm-user',
        extra: _usernameController.text,
      );
    // (7)
    } on NotAuthorizedException {
      setState(() {
        _isLoading = false;
        _errorMessage = 'Username or password is wrong. Please try again';
      });
    } on Exception catch(error) {
      setState(() {
        _isLoading = false;
        _errorMessage = 'An unexpected error has happened. Check the logs for detail';
      });
      logger.error(error.toString());
    }
    _usernameController.clear();
    _passwordController.clear();
  }
}