title: Validate facebook oauth token in background
body: <p>I'm accessing Facebook in a background thread from my app. I initally logged in the user from my activity and stored the oauth token. It is possible that the oauth token has expired in the meantime, even with offline access. How could I check for valid oauth token with the Facebook Android SDK?</p>
  
  <p>When I create a new Facebook object the oauth field is not set. I could set it from my stored token, but I didn't store the session expiry time. Therefore, looking at the source code, both <code>isSessionValid()</code> and <code>request()</code> will fail. I cannot <code>authorize()</code> the user from the background thread with a popup log-in dialog.</p>
  
  <p>Does that mean that I cannot check for valid token via the SDK?</p>