I have just come across Google App engine and am trying to develop a site on it. Part of the site should allow users to log in. I plan to offer two options.
When using my own log in form I can force a unique identity to be created through an email address/user name field, etc. but how can I get a unique identity from an open id user? Are they guarantied to have supplied an email - as in will the user service give me a user object that is guarantied to have an email?
Thanks a lot for any advice
To get the unique identifier for a user, use User#getUserId().
Returns an opaque string that uniquely identifies the user represented by this User object.
In case of open ID account, you can also use User#getFederatedIdentity(), however, I would say that it does not have to return always the unique identifier.
There are two flavors of provider types: direct providers like Google and Yahoo! require only a generic federated identity that has no username associated with it.
In contrast, Flickr, WordPress, Blogger, and LiveJournal are known as username providers because all require you to provide a URL which does.
See more details here.
Anyway there is also a possibility to store the user object as a whole. This is supported out of the box by App Engine and Datastore.