mobile-app/lib/custom_model/user_request.dart

import 'package:json_annotation/json_annotation.dart';
part 'user_request.g.dart';

@JsonSerializable()
class UserRequest {
  final String username;
  final String password;
  UserRequest({this.username, this.password});

  factory UserRequest.fromJson(Map<String, dynamic> json) =>
      _$UserRequestFromJson(json);
  Map<String, dynamic> toJson() => _$UserRequestToJson(this);
}