Janrain, a provider of user ID management services, estimates Facebook (FB) accounts for 45% of all logins on 3rd-party sites/apps that involve an outside "identity provider," and Google (GOOG) 33%. Yahoo and Twitter are tied for #3 at a mere 7% apiece.
Facebook's login share surged from 2010-2012, partly at Google's expense, and peaked in Q3 of last year at 54%. Google, which bottomed at 33% that quarter, has made up some ground since then. The company's efforts to promote Google+ sign-ins are a key reason.
In addition to keeping users logged in to a site/platform, login services help drive the sharing of content from the sites/apps that rely on them, and give service providers user activity data that can be used for ad targeting.
The report comes as Facebook attempts to grow its login count by striking a public Wi-Fi partnership with Cisco. The companies will provide free Wi-Fi to retailers, hotels, and other businesses ... but users will have to log in with a Facebook ID first.