gistfile1.dart

 //in class auth
 Future<void> _authenticate(
      String email, String password, String urlSegment) async {
    final url =
        'https://www.googleapis.com/identitytoolkit/v3/relyingparty/$urlSegment?key=hjey';
    try {
      final response = await http.post(
        url,
        body: json.encode(
          {
            'email': email,
            'password': password,
            'returnSecureToken': true,
          },
        ),
      );
      final responseData = json.decode(response.body);
      if (responseData['error'] != null) {
        throw HttpException(responseData['error']['message']);
      }
      _token = responseData['idToken'];
      _userId = responseData['localId'];
      _expiryDate = DateTime.now().add(
        Duration(
          seconds: int.parse(
            responseData['expiresIn'],
          ),
        ),
      );
      
      _autoLogout();
      notifyListeners();
      final prefs = await SharedPreferences.getInstance();
      final userData = json.encode(
        {
          'token': _token,
          'userId': _userId,
          'expiryDate': _expiryDate.toIso8601String(),
        },
      );
      prefs.setString('userData', userData);
    } catch (error) {
      print(error);
      throw error;
    }
  }

  Future<void> signup(String email, String password) async {
    return _authenticate(email, password, 'signupNewUser');
  }

  Future<void> login(String email, String password) async {
    return _authenticate(email, password, 'verifyPassword');
  }
  
  
// in Raised Button

 Future<void> _submit() async {
    if (!_formKey.currentState.validate()) {
      // Invalid!
      return;
    }
    _formKey.currentState.save();
    setState(() {
      _isLoading = true;
    });
    try {
      if (_authMode == AuthMode.Login) {
        // Log user in
        await Provider.of<Auth>(context, listen: false).login(
          _authData['email'],
          _authData['password'],
        );
      } else {
        // Sign user up
        await Provider.of<Auth>(context, listen: false).signup(
          _authData['email'],
          _authData['password'],
        );
      }
    } on HttpException catch (error) {
      var errorMessage = 'Authentication failed';
      if (error.toString().contains('EMAIL_EXISTS')) {
        errorMessage = 'This email address is already in use.';
      } else if (error.toString().contains('INVALID_EMAIL')) {
        errorMessage = 'This is not a valid email address';
      } else if (error.toString().contains('WEAK_PASSWORD')) {
        errorMessage = 'This password is too weak.';
      } else if (error.toString().contains('EMAIL_NOT_FOUND')) {
        errorMessage = 'Could not find a user with that email.';
      } else if (error.toString().contains('INVALID_PASSWORD')) {
        errorMessage = 'Invalid password.';
      }
      _showErrorDialog(errorMessage);
    } catch (error) {
      const errorMessage =
          'Could not authenticate you. Please try again later.';
      _showErrorDialog(errorMessage);
    }

    setState(() {
      _isLoading = false;
    });
  }