Check out the Xamarin Azure Mobile Services demo here
https://github.com/xamarin/azure-mobile-services
Here is a class that uses the authentication method
Authentication is not currently supported for Android devices. That includes applications written in Java and C# using Monodroid.
The only Mobile Services feature currently supported is Data Services using JSON.
The Microsoft SDK hasn't been released for Android yet.
Sit tight though as Azure development is moving swiftly and this feature should be added soon.
Remember the Azure Mobile Services is still in preview and many features available in Windows Phone are not yet available on Android.