Facebook has joined the foundation behind the OpenID scheme - an online log-in process that gives users the ability to sign into multiple sites with a single user ID.

What's surprising about the development is that OpenID is seen as a rival service to Facebook's own "Connect" offering, and it's so far unclear as to how Facebook plans to move forward with the two schemes.

Announced via a blog post, Facebook's Mike Schroepfer says that Facebook Connect has seen 4000 sites and desktop applications with the service, but reveals:

"We're happy to announce today that we are formalizing our support of the OpenID Foundation by officially joining the board. 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".

Facebook will reveal more at an OpenID Design Summit at its headquarters in Palo Alto next week.