Xamarin.Auth is a great component for programming OAuth. However, it isn't Forms and PCL friendly. I've created a GitHub project which demonstrates how to use a wrapper class to expose Xamarin.Auth functionality for use with Forms and PCL.
Synopsis: Complete C# cross-platform mobile app. Demonstrates requesting of OAuth credentials enabling execution of APIs. Implements Xamarin.Auth in Xamarin.Forms in a natural, PCL-like way. Uses JSON data file to provide a selection of OAuth logins. Providers include Amazon, Facebook, Google, and many more.
1. Easy and powerful implementation of Xamarin.Auth in Xamarin.Forms.
2. Complete C# cross-platform mobile app [not yet].
3. Use Xamarin.Auth as if it was a native PCL library. No need to push logic into platform dependent files.
4. Demonstrates usage of most Xamarin.Auth members.
5. Compatible with (most) OAuth1 and OAuth2 providers.
6. Uses an easily configurable embedded JSON file to drive execution. File contains OAuth providers, credentials, URLs and much more.
7. Working examples of calling many different OAuth providers.
8. Contains necessary logic to support quirky OAuth implementations.
9. Easily adaptable Xamarin.Auth implementation ready for inclusion in your projects.
10. Wraps Xamarin.Auth in PCL for easy use.
11. Designed to be compatible with existing and future versions of Xamarin.Auth.
12. Easy way to test OAuth implementations. Simply enter a new OAuth provider implementation in the JSON file.
13. Demonstrates use of saving/reusing/deleting credentials to minimize repeated authentications.
14. Demonstrates use of refreshing expired authorizations [not yet].
15. Demonstrates use of binding to Xamarin.Forms controls.
16. Easier to use than WebView and non-PCL solutions.
17. Complete source code provided. No restrictions on use.