Xamarin forms ios : No done/cancel button showing

When I present view controller from Xamarin auth Get ui then not able to get cancel or done button. Anyone have idea why it is so?
This is how I do that in Xamarin forms ios renderer =>
var auth = new SocialAuthenticationService(CommonConstants.FacebookClientId, CommonConstants.Scope, CommonConstants.AuthorizeUrl, CommonConstants.RedirectUrl);
var oAuth2Authenticator = auth.GetAuthenticator();

            var viewControllerToPresent = oAuth2Authenticator.GetUI();
            PresentViewController(viewControllerToPresent, true, null);

Xamarin Auth version=1.6.0.1
Xamarin forms version=Xamarin.Forms.2.3.4.270