Two Different Google OpenID URLs

Question

I just realized there are two google open id urls I can find online.

• https://www.google.com/accounts/o8/id
• https://www.google.com/accounts/o8/ud

Would you please tell me which one is the right one to use?

Answer 1

• https://www.google.com/accounts/o8/id is an XRI OpenID identifier that can be used when a web site asks you for you OpenID URL. It's technically not your own OpenID URL (yours will have some unique string appended) but the document it serves contains all the infomation an OpenID consumer needs.
• https://www.google.com/accounts/o8/ud is the actual URL of Google's OpenID provider. Not much use to you but an OpenID consumer will be sending request to that URL as part of the OpenID flow.

In short, when a website asks you for your OpenID identifier, you can enter https://www.google.com/accounts/o8/id. The website will then behind the scene do a GET on that URL which will return an XRDS document. This XRDS document contains the URL of Google's OpenID provider which is https://www.google.com/accounts/o8/ud and will then proceed with the OpenID flow.

See http://openid.net/specs/openid-authentication-2_0.html for full info about OpenID identifiers and providers.