After some googling I guess I found SSO is not the same as OpenID :)
Did some quick googling and found these:
- http://www.single-signon.com/en/home.html (GPL)
- https://github.com/jasny/SSO (public domain)
- http://share.ez.no/learn/ez-publish/using-a-sso-in-ez-publish
- http://simplesamlphp.org/
- http://www.yiiframework.com/wiki/135/single-sign-on-across-multiple-subdomains/
