Get OpenID URL with OAuth

Question

I used OpenID to log in a web service. Now I will change this to OAuth!

With OAuth I could receive also an identify:

0101201... (Google ID)

But I need the OpenID identify for the database - like:

https://www.google.com/accounts/o8/id?id=Hf5S...

How could I receive this value with an request?

Thanks very much!