Control look of OAuth Dialog

[JoeHershman]

Hi,

I setup a Xamarin Forms application to use OAuth authentication in an iOS application based on the OAuth Security sample.  Everything works great, but I am wondering if there is a way to have more control on the look of the popup.  

It would great to change the sizing a little.  Also I would like to remove the buttons for the other login methods (github, facebook, etc.)

Thanks

-Joe