Retrofit use

api interface

public interface Api {
  @POST("/users/sign_in") Observable<Response> login(@Body Login login);
}

client

    client.login(login)
        .observeOn(AndroidSchedulers.mainThread())
        .subscribeOn(Schedulers.io())
        .subscribe(new Observer<Response>() {
          @Override public void onCompleted() {
          }

          @Override public void onError(Throwable e) {
          }

          @Override public void onNext(Response response) {
            User user;
            try {
              user = (User) gsonConverter.fromBody(response.getBody(), User.class);
            } catch (Exception e) {
              onError(e);
              return;
            }
            //...
          }
        });

gistfile1.java

public class Login {
  private String email;
  private String password;
  private String fbToken;
  private String gplusToken;
  private String audienceToken;

  public Login(String email, String password) {
    this.email = email;
    this.password = password;
  }

  public Login() {
  }
  
  //...
}