title: Check if a device google account is authenticated, only then allow access to my offline app
body: <p>I have a private app which works totally offline (i.e. no server data sent/recieved), however I have a need to restrict it only to users with a valid Google account on their phone.  I can get make sure there is a suitable account on the phone by iterating a list of phone accounts, but is it possible to check the account is valid/authenticated without me having to introduce the full OAuth process?  I have no need to get a cookie or send any data to a server.</p>
  
  <p>Ideally I'd like to do something like: 
  1. Check with the account manager for an auth token.
  2. If token recieved then allow access to the app.
  Currently without any checks via the account manager, anyone could create a fake account on the phone and then gain access even if they put in a email/password and they would never be authorised.</p>
  
  <p>I hope I've explained this clearly.  As my app has no network connectivity so I would like to avoid adding any of my own network/oauth checking.</p>