OpenID is a single sign-in infrastructure that potentially alleviates the need to create new passwords and user names for every new site one joins or visits. There’s been lots of discussion about OpenID and who’s in, who’s almost in, and so on. Today, Yahoo formally joined (and fully legitimized) the effort. Microsoft Passport was originally conceived to be a similar system but failed to gain support and broad adoption. OpenID is supported by an independent foundation and not aligned with any particular company. In addition to Yahoo, here’s the list of sites that currently support OpenID login.

While it’s a great convenience for end users and intended to “open up” the process of signing in to sites, the strange paradox of OpenID is that it potentially reinforces a relationship between a user and his/her open ID “home.” That is, the master login that a person uses: AOL screenname, WordPress login, or, now, Yahoo login. As Yahoo explains: When you are on a web site that supports OpenID login, simply look for a Yahoo! login button. Or if you see a text box with an OpenID icon, simply type in “yahoo.com”. You will be sent to Yahoo! to verify your Yahoo! ID and password, and then you will be able to continue on.

Yahoo’s 248 million registered users globally now become part of the system. Google, LinkedIn, and Facebook have all been associated with discussions to support OpenID, though have not formally announced that support. Now, with Yahoo’s participation secured, it should just be a matter of time before other big names join (AOL and Plaxo are also currently on the list of supporting companies.)

OpenID is thematically related to another, broader issue: data portability. The latter is very much like the idea of a unified login/password system except that it applies to data much more broadly. In theory, “data portability” would allow interoperability among various participating sites. However, the issues surrounding data portability are much more complex than OpenID. At the heart of the debate over data portability are questions of who “owns” or controls data and user privacy.

But there are also competitive issues that no doubt create ambivalence too: smaller or “insurgent” sites might like the idea, while larger or “incumbent” sites might not as much. An example of this was the recent Plaxo-Facebook flap that had Plaxo scraping email addresses from Facebook, and the latter’s displeasure with that effort.

If adopted and implemented, data portability would theoretically destroy the remaining vestiges of the “walled gardens” or semi-walled gardens on the internet.

Related Topics: Yahoo: General

About The Author: Greg Sterling is a Contributing Editor at Search Engine Land. He writes a personal blog Screenwerk, about SoLoMo issues and connecting the dots between online and offline. He also posts at Internet2Go, which is focused on the mobile Internet. Follow him @gsterling. See more articles by Greg Sterling