Pablo M. Cibraro (aka Cibrax) recently published a post on creating an OAuth channel for WCF RESTful services.  If you are not familiar with OAuth, it focuses on a particular security scenario where you want to grant (limited) access to secured resources to a third party.  Picture (pun intended) exposing your Flickr photos to a third party service for printing.  You would not want to provide them with your login credentials, nor would you want to grant them carte blanche access to your account.  Enter OAuth.  Take a look at this post for all of the details.

Regards