title: Java example of how to log in to Google App Engine with a Facebook account using OAuth
body: <p>I searched a lot, read many blogs, articles, tutorials, but until now did not get a working example of using a Facebook account to log in to my application.</p>
  
  <p>I know that I have to use OAuth, get tokens, authorizations, etc...</p>
  
  <p>Can anyone share an example?</p>