title: Execute a Volley request after another one is finished
body: <p>I have two Volley requests. The first request authenticates the user; the second one gets data from the server.</p>
  
  <p>If I send a <code>GET</code> request and the user is not authenticated, I want to fire the first request, authenticate the user and then keep executing the second one once the user is successfully authenticated.</p>