Xamarin.Auth and Google Drive API: OAuth2Authenticator not IsAuthenticated

Question

So this is how I launch my login page:

this.OnGoogleDrive = new Command(() =>
            {
                var presenter = new OAuthLoginPresenter();
                presenter.Login(auth);
            });

And this is how I define my Authenticator:

var auth = new OAuth2Authenticator(
              this.clientId,
              string.Empty,
              scope,
              new Uri("https://accounts.google.com/o/oauth2/v2/auth"),
              new Uri(redirectUrl),
              new Uri("https://www.googleapis.com/oauth2/v4/token"),
              isUsingNativeUI: true);

So my app opens a page where the Google login page appears and authorizes my scope. At the very end, it shows me a code that I had to copy paste. So far I thought that the page would instead make IsAutheticated true. But when I got to the method handling the Completed event, it is read as false. Why is that? Was I using the wrong way to open the Login page?