Some time ago I was hired to coach a project where also oAuth was required. Lucky the client was so kind to let us opensource the code.
The resulting, CodeIgniter, library can be found on GitHub. It’s written for CodeIgniter, but with very small modification it can be used with any PHP framework.
Supports
Facebook (oAuth v2)
Twitter (oAuth v1)
LinkedIn (oAuth v1)
Features
Let users login into your site using their Facebook, Twitter or LinkedIn login