I have Android client to my AppEngine server, both using Google Accounts. I would like to use AccountManager for getting accessToken for OAuth. So far I\'m using Client
As of today you can use Google Play Services API on android to do Oauth 2.0 authentication on android. You could then use the method described by @nivco to get the userinfo on appengine. I have not done this yet, but I plan tp do exactly what your talking about.
https://developers.google.com/android/google-play-services/authentication