US Patent 9231940 Credential linking across multiple services

A first server device may receive, from a user device, a request to authenticate the user device for a first service using authentication credentials for a second service that is different than the first service; provide the authentication credentials to a second server device that provides the second service; receive from the second server device, and when the authentication credentials are valid for the second service, user information relating to a user of the user device; and provide, to the user device, an authentication response, associated with the user information, that provides authentication of the user device for the first service.