Native Google Auth setup for Simple Auth. https://github.com/clancey/simpleauth

GoogleSimpleAuth.cs

//#iOS Setup
// In Appdelegate override OpenUrl (UIApplication app, NSUrl url, NSDictionary options) and add
return SimpleAuth.Native.OpenUrl(app, url, options);

//#Android
//In Activity override OnCreate and add
SimpleAuth.Providers.Google.Init(this.Application);

//In Activity override  OnActivityResult(int requestCode, Result resultCode, Intent data) and add
SimpleAuth.Native.OnActivityResult (requestCode,resultCode,data); 

//Make Api calls
var api = new GoogleApi("google","clientid","clientsecret");
var user = await api.GetUserInfo();

//For more info: https://github.com/clancey/simpleauth