http://www.developer.nokia.com/Community/Wiki/Foursquare_authentication_in_Windows_Phone_application
Google+:
http://www.developer.nokia.com/Community/Wiki/Google%2B_authentication_in_Windows_Phone_application
Linkedin:
http://www.developer.nokia.com/Community/Wiki/LinkedIn:_Authentication_and_viewing_own_basic_profile
Facebook:
http://www.developer.nokia.com/Community/Wiki/Facebook_authentication_in_Windows_Phone_application