title: Blocking request interceptor with Retrofit?
body: <p>Is there a nice way to implement "blocking" request interceptor?</p>
  
  <p>The main idea is that all requests should be intercepted and added additional header - <code>token</code>.</p>
  
  <p>If <code>token</code> does not exist yet it should be retrieved first, then added to that request and cached for future used. <code>token</code> is retrieved via API call.</p>
  
  <p>I've tried to do synchronous request, but, that produces <code>android.os.NetworkOnMainThreadException</code>. And implementing with <code>in_progress</code> flags it doesn't look nice.</p>