public LoginPage : ContentPage
{
   public OnLoginDidCompleteDelegate OnLoginDidComplete { get; set; }
   protected LoginViewModel ViewModel { get; set; }

   public LoginPage()
   {
      InitializeComponent();
      BidingContext = ViewModel = new LoginViewModel();

      // Relay callback from ViewModel
      ViewModel.OnLoginDidComplete = (accessToken, user) => {
         this.OnLoginDidComplete?.Invoke(accessToken, user);
      };
   }
}