Scenario

In this scenario you are developing a Windows Phone 7 (WP7) application that consumes RESTful WCF service. You need to integrate Internet Identity Providers (IdP's) such as Live ID, Facebook, Google, Yahoo! and Open ID 2.0 identity providers for authentication purposes.

WP7 application with WCF (REST) service as its back end.
Internet Identity Providers (IdP's) such as Live ID, Facebook, Google, Yahoo!, Open ID 2.0

Solution Approach

WP7's Web Browser control and ACS used to solve this scenario.

WP7 application hosts Web Browser control that displays IdP's and also perform actual sign in dance resulting in receiving SWT token from ACS upon successful authentication.
The SWT token handed to the WP7 application from the hosted WebBrowser control.
The SWT token sent to the WCF (REST) service.
The WCF (REST) service validates and parses the token.

Analysis

Internet Identity providers are optimized for web applications vs. web services. This is the reason why WebBrowser control is used in this scenario to accomplish the redirects required for sign in process.