Login to a website using LinkedIn .
http://developer.linkedin.com/documents/sign-linkedin
Widgets
Get access to data on 3,578 websites that are LinkedIn Sign In Button Customers. We know of 618 live websites using LinkedIn Sign In Button and an additional 2,960 sites that used LinkedIn Sign In Button historically and 335 websites in the United States.
Get a list of 3,578 websites using LinkedIn Sign In Button which includes location information, hosting data, contact details, 618 currently live websites and an additional 2,713 domains that redirect to sites in this list. 2,960 sites that used this technology previously and 335 websites in the United States currently using LinkedIn Sign In Button.