Endless problems with Xamarin.Auth on Android

I would guess that in my last 4 weeks of creating the Golf80 app – about third of the time has been spent on 3rd party authentication (Google, Facebook, … ) and most of that time on Google authentication on Android.  A lot of lessons learned and googled.  Most of the examples are pretty thin, and explain the simple parts but leave out detailed explanation of the callback and url interception process.  My favorite explanation (note to self) is probably this one:  https://www.codementor.io/@ravitejalingineni/oauth-explained-with-xamarin-forms-q2zomkhda