Update: Facebook just opened up FB Connect as well in a self-serve fashion. It’s mano-a-mano.

The battle over who will control access to your online identity is heating up. In the wake of more and more partners finally starting to take a shine to Facebook’s competing FB Connect (which we just implemented on Techcrunch), Google’s Friend Connect is now in an open beta. Before it was in a limited preview release, but now any website can add Google Friend Connect as a login option.

Google Friend Connect is OpenSocial’s answer to Facebook Connect. It lets other websites accept a member’s OpenSocial OpenID username and password to log into their sites. More importantly, it also lets websites access users’ social data, which includes friend lists, profile information, feed messages, reviews, ratings and the like.

Since it is based on OpenID, visitors to a Website that adds Friend Connect code will be able to sign in using their Google, Yahoo, AIM, or OpenID usernames and passwords. The Websites will also be able to add any OpenSocial apps developed by third parties. And it supports the OAuth data portability standard.

When you drill down into the technical details, there are some differences between Friend Connect and FB Connect. But ultimately, what is at stake here is what will become the identity and data portability standard on the Web, and who will control it. While Friend Connect is taking a more open-standards approach, Facebook has the users and the momentum. Who are you betting on?