Social networking giant Facebook has implemented support for OpenID logins. The move reflects Facebook's growing support for interoperability and open standards. It's also a win for OpenID, which is rapidly becoming ubiquitous.

OpenID is a distributed authentication system that allows a single login to be used with multiple Web services. Originally developed for LiveJournal in 2005, the system has gained significant traction and is now supported by a growing number of large companies, including Microsoft, Google, IBM, and Yahoo. Many OpenID adopters, however, only support the provider part of the protocol—meaning that you can use your credentials from their service as your OpenID identity but you can't use OpenID to log into their service.

Facebook is doing the opposite. In an announcement on Monday, the company revealed that it will become an OpenID "relying" party and that users will consequently be able to register for Facebook using their authentication credentials from compatible third-party services. This makes Facebook the single largest Web service to implement relying party support. It's a somewhat intriguing move, because the site offers a service called Facebook Connect that is designed to compete with OpenID as an identity provision service.

In recent months, Facebook has been making a strong effort to expose some of the capabilities of its platform through open standards alongside its own APIs. Another compelling example of this trend at Facebook is the recent launch of the website's open stream API. In addition to making the content of user activity streams accessible to third-party software developers through Facebook's conventional REST API and FQL query system, the company also decided to supply an XML feed that uses Atom Activity Extensions, an emerging draft-status standard that is built on top of the Atom syndication format

Facebook has traditionally had a reputation for being a walled garden, and its third-party application platform is seemingly engineered to maximize lock-in. The company's newfound enthusiasm for interoperability is a promising sign that Facebook is undergoing a cultural shift and is beginning to appreciate the value of playing well with others.

It's worth noting that the move isn't entirely motivated by a love for open standards. Facebook has discovered that the practical value of OpenID extends beyond interoperability. In the company's official announcement, Facebook engineer Luke Shepard says that OpenID has helped to streamline the registration and login process, lowering the barrier to entry for new users. This helps Facebook boost its audience and increases the percentage of users that will stick with the service after signing up.

"Over the past several months, we've taken a number of steps that help to build a scalable, secure, and sustainable framework, one that further defines what it means to be an OpenID relying party," he wrote. "In tests we've run, we've noticed that first-time users who register on the site with OpenID are more likely to become active Facebook users. They get up and running after registering even faster than before, find their friends easily, and quickly engage on the site."

He says that users can now register for Facebook through OpenID, and existing users will also be able to link their Facebook accounts with an OpenID identity. He characterizes these features as Facebook's first steps as a member of the OpenID community. Facebook joined the OpenID Foundation Board earlier this year and intends to participate in the ongoing evolution of the standard.