You've been able to do that with OpenID for the last few years, that's why you can just have buttons for Yahoo, Google, or myOpenID instead of needing to type i

You've been able to do that with OpenID for the last few years, that's why you can just have buttons for Yahoo, Google, or myOpenID instead of needing to type in joe.myopenid.com or google.com/id/aoeiasnexhtsanogysaeig==