Is it possible to get users email by hosting gadget on appspot?

Google App Engine provides its User API service, using which you can allow people with Google Accounts to easily access your application. It works in a manner much similar to Google's other login services. When you login, you are taken to a central page, common for all google services and then after you have authenticated yourself, you are redirected back to the service.

Since Google uses a central page for login and logout and it is a cookie based authentication, it might trigger question - if someone is logged into gmail or orkut or other such google service is it possible to get their Google Accounts using App Engine's Users API? In order to do so, i deployed an application on App Engine, which would write "hello World!" on the canvas. This gadget XML is generated pragmatically and at the backend, there is a code which checks for a valid Google Account Holder.

The corresponding code goes as follows:
(There is no space at line 39, the space are mentioned here to go according to the syntax highlighter)




Upon deploying the gadget on orkut and gmail, i found that everytime the gadget loads, i just see a new entry in the Log, saying "User is None".

This means that you can authenticate only users for your own domain/application, not for all of the Google products services :-)

The complete source code of the application can be found at its Google Code repository http://code.google.com/p/codecontrol-samples/source/browse/user-authentication/src/.