User ModernHttpClient on Xamarin Targets

[anujb]

I'm not sure whether this is feasible, but it would eliminate a ton of potential issues with the Microsoft HTTP Client libraries on Xamarin.

[moonpyk]

@anujb As of Xamarin.Android 6.1 you can do that by overriding an env variable in your app :

https://developer.xamarin.com/releases/android/xamarin.android_6/xamarin.android_6.1/#Native_HttpClientHandler