I just saw <http://uservoice.com/login>. It uses Google accounts, [Myspace](http://en.wikipedia.org/wiki/Myspace), Yahoo, [OpenID](http://en.wikipedia.org/wiki/OpenID) and all to sign in customers into its site? Can I do that?

I mean, customers need not register to my site. They can just sign in with their accounts on the above sites.

If you've a solution, I'd prefer a PHP and MySQL based one.