Facebook has joined the board of the OpenID Foundation, the company has announced. The move is a ringing endorsement of OpenID, which already has the corporate backing of Google, Microsoft, IBM, PayPal and other web heavyweights.

In a blog post Thursday, Facebook’s Mike Schroepfer (formerly of Mozilla), said, “It is our hope that we can take the success of Facebook Connect and work together with the community to build easy-to-use, safe, open and secure distributed identity frameworks for use across the web.”

Prior to the announcement, Facebook was seen as a sideline player — and even a disruptive presence — for the open-source single sign-on technology. Late last year, Facebook launched its own trusted authentication technology for letting its users log in and participate on other websites. The company’s system, Facebook Connect, has since been implemented by around 4,000 websites, including numerous high-profile destinations like CitySearch and TechCrunch.

With Facebook Connect, the company came up with an elegant, easy-to-use experience that effectively solved several of OpenID’s problems with user experience, trust and security. However, Facebook Connect was built with proprietary code, and was therefore largely incompatible with competing open-source technologies like OpenID.

The resulting effects of this partnership on data portability are unclear. And whether Facebook and the rest of the internet are now part of the same big happy family remains to be seen. But for those worried about Facebook Connect derailing OpenID or causing it to die on the vine, this is huge.

Certainly, we can expect OpenID’s public profile and reach to get a boost. Also, a post on OpenID’s website trumpets Facebook’s dedication to improving OpenID’s user experience.