Login to a website using LinkedIn .
http://developer.linkedin.com/documents/sign-linkedin
Widgets
Get access to data on 3,556 websites that are LinkedIn Sign In Button Customers. We know of 664 live websites using LinkedIn Sign In Button and an additional 2,892 sites that used LinkedIn Sign In Button historically and 349 websites in the United States.
Get a list of 3,556 websites using LinkedIn Sign In Button which includes location information, hosting data, contact details, 2,481 currently live websites which includes 1,817 domains that redirect to sites in the list. 2,892 sites that used this technology previously and 349 websites in the United States currently using LinkedIn Sign In Button.