Identify User with common identifer for windows azure mobile services & MVC web application

Identify User with common identifer for windows azure mobile services &
MVC web application

Here is what I want to do.
I want to have a MVC web application that I can user to administer tables
in my SQL server database (windows azure). I want to authenticate with a
3rd party login (google, twitter, facebook etc).
I want to have a mobile application that makes use of windows azure mobile
services to access and modify those tables. The mobile app will log in
with the same providers as above.
The problem: when I log in with the MVC application I have access to the
username and email address.
When I log in with the mobile application I get access to a userId
="google":{ "userId":"Google:my-actual-user-id",
"accessToken":"the-actual-access-token" } on the mobile service side but
not the email address or username.
So if I want to write a Server side script(azure mobile service) to get
data from the tables, what should I use as the unique user identifier??
The MVC application does not have access to the userid the mobile
application gets on login, and the mobile application does not have access
to the username or email address available via the MVC
login(OAuthWebSecurity)
I found this link:
http://blogs.msdn.com/b/carlosfigueira/archive/2012/10/25/getting-user-information-on-azure-mobile-services.aspx
But looks like you cannot even get the google email using this…. So still
no way to uniquely identify the user!!
Thanks for any help