The recently released version of Facebook’s Comments Box social plugin for third-party websites now accepts AOL accounts for login. Initially the plugin only allowed Facebook and Yahoo! for login, though we discovered there was live code for Twitter and Google logins present but inactive.

The additional login option will make the Comments Box accessible to a larger user base, but some might say that AOL’s willingness to be a login option is a signal that is has accepted its fate as a second-tier identity provider.

It appears that Facebook is reaching Comments Box login agreements with sites who have reciprocated by allowing Facebook as a login option on their sites or services. AOL allows users to sign in to it’s AIM instant messaging and some other service  with Facebook, and Yahoo! recently enabled Facebook as a login and account registration option across its properties.

The Comments Box has brought up a difficult question for the web’s largest services and social networks. By refusing to be a Comments Box login option, they force their users to employ another service provider’s credential in order to comment, but they in turn don’t have to permit Facebook as a login option. This allows them to own the registration information of anyone benefiting from their services.

On the other hand, by agreeing to Facebook’s terms and becoming a Comments Box login option, their users won’t have to choose another’s service credentials, but they usually must permit Facebook to colonize their site with its own login buttons.

Facebook is winning the identity game, and Yahoo! and AOL both now seem to have folded. The question remains whether Google or Twitter will concede to Facebook’s terms, work out a more evenhanded deal, or if they’ll continue to stay autonomous and try to themselves become the premier online ID.

[Thanks to David Sanger for the tip.]