Map<String, dynamic> _convertJsonToMap(String response) {
    return json.decode(response);
  }

  Observable<User> _getUserDetails(String username, String password) {
    return Observable.fromFuture(_get('/login?username=$username&password=$password'))
        .map((res) {
          _authToken = res.body.token;
          return User(res.body.data);  /** Using manual Serialization in User model **/
    });
  }

  Observable<User> _storeDetails(User user) {
    return Observable.fromFuture(_post(endPoint, data))
        .map((res) {
          return serializers.deserializeWith(UserResponse.serializer,
        _convertJsonToMap(res.body)); /** Using Built Value for Serialization **/
    });
  }