PopModalAsync() returns to the same page is iOS

Hi,

I have a custom page with a pagerenderer for a google oauth2 login. But when the login is succesfull I need to return to my previous page. This is my code:

[assembly: ExportRenderer(typeof(GoogleLoginPage), typeof(GoogleLogin_iOS))]

namespace iBridge_RandstadMetaApp.iOS
{
    public class GoogleLogin_iOS : PageRenderer
    {
        public override void ViewDidAppear(bool animated)
        {
            base.ViewDidAppear(false);

            var auth = new OAuth2Authenticator(
                clientId: App.GoogleApiClientId,
                clientSecret: App.GoogleApiClientSecret,
                scope: "email",
                authorizeUrl: new Uri("https://accounts.google.com/o/oauth2/auth"),
                redirectUrl: new Uri(App.GoogleApiRedirectUrl2),
                accessTokenUrl: new Uri("https://accounts.google.com/o/oauth2/token"),
                getUsernameAsync: null
            );

            auth.Title = App.GetTextFromKey("Login");
            auth.AllowCancel = false;

            auth.Completed += (sender, eventArgs) =>
            {
                if (eventArgs.IsAuthenticated)
                {
                    // Use eventArgs.Account to do wonderful things
                    string code = "";
                    eventArgs.Account.Properties.TryGetValue("access_token", out code);
                    Console.WriteLine("ac: " + code);

                    App.GoogleApiAccesToken = code;

                    eventArgs.Account.Properties.TryGetValue("refresh_token", out code);
                    Console.WriteLine("rc: " + code);

                    NavHelper.Nav.NavigateToValidationPageAction.Invoke();
                }
            };

            PresentViewController(auth.GetUI(), false, null);
        }
    }
}


public class NavHelper
    {
        static volatile NavHelper _nav;
        static object _SyncRoot = new Object();
        public static NavHelper Nav
        {
            get
            {
                if (_nav == null)
                {
                    lock (_SyncRoot)
                    {
                        if (_nav == null)
                        {
                            _nav = new NavHelper();

                        }
                    }
                }

                return _nav;
            }
        }

        public NavigationPage NavPage { get; set; }

        public Action NavigateToValidationPageAction
        {
            get
            {
                return new Action(() =>
                {
                    App.LoginOk = true;
                    //NavPage.Navigation.PushModalAsync(new ValidationPage());
                    if (Device.OS == TargetPlatform.iOS)
                    {
                        NavPage.Navigation.PopModalAsync();
                        //NavPage.Navigation.PushModalAsync(new ValidationPage());
                    }
                    else if (Device.OS == TargetPlatform.Android) {
                        //NavPage.Navigation.PopModalAsync();
                        NavPage.Navigation.PushModalAsync(new ValidationPage());
                    }
                });
            }
        }
    }