When you write enterprise mobile applications you’re always confronted with authentication. There are a lot of examples that show you how you can authorize the user with Facebook. I don’t know about other countries, but in Belgium enterprise companies don’t let you login on their corporate environment with your Facebook account. You can use Xamarin.Auth for authorization with other services than Facebook, but if the authorization flow is a bit different, you can’t use it anymore.
A while ago a colleague asked me how to test a REST API when you need a token to use the API. He just wanted to verify some data and didn’t want to write any code. You’ll need to do some configuration, but once it’s setup the REST calls become painless.