title: how does facebook authentication on mobile devices work?
body: <p>I am trying to understanding how the authentication of fb happens on mobile devices(ios/android)?</p>
  
  <p>only for the first time when i installed the fb app, i entered the username/pwd. Thats it. from next time onwards, it will auto authenticate itself.</p>
  
  <p>1) Does the fb mobile app stores the username/pwd on the device in any file? 
  2) will it use oauth or similar token mechanism? if so, where does the token stored on the device. </p>
  
  <p>I guess, my question is, in which memory/path/filename it is stored, so that it is secured and cannot be accessed by other apps/root users.</p>
  
  <p>Thanks much</p>