i'm sorry but i've been searching a long time and haven't been able to find Openid authentification for Joomla 2.5 and 3.1
There are several J2.5 extensions (should work fine on J3.0), which you can find below that offer OpenID.
extensions.joomla.org/search?q=openid
isn't it possible to add it on CB Connect ?
I've no plans at this time to implement OpenID. That's not to say it'll never be implemented though. I will re-review its implementation after CB 2.0.