code: def deauthorize_application(request):
      
      if request.facebook:
          user = User.objects.get(
              facebook_id = request.facebook.signed_request.user.id
          )
  
          user.authorized = False
          user.save()
  
          return HttpResponse()
      else:
          return HttpResponse(status=400)
docs: When a user deauthorizes an application, Facebook sends a HTTP POST request to the application's
      "deauthorization callback" URL. This view picks up on requests of this sort and marks the corresponding
      users as unauthorized.