title: django-rest-framework: add additional permission in ViewSet update method
body: <p>I have the following code:
  </p>
  
  <pre><code>class UsersViewSet(viewsets.ModelViewSet):
      model = Users
      permission_classes = (IsAuthenticated,)
  
      def update(self, request, *args, **kwargs):
          return super(UsersViewSet, self).update(request, *args, **kwargs)
  </code></pre>
  
  <p>The question is:</p>
  
  <ul>
  <li>how can I add additional Permission only for update method? (need to get isAuthenticated + Permission)</li>
  <li>overwrite permissions only for update method? (need to get only Permission without isAuthenticated)
  other methods in viewset should have IsAuthenticated permission</li>
  </ul>
  
  <p>Can I make it with decorator?Or anything else?</p>
  
  <p>Wanna get something like that:
  </p>
  
  <pre><code>@permission_classes((IsAuthenticated, AdditionalPermission ))
  def update:
      pass
  </code></pre>
  
  <p>But if i write this code the second permission is not checked through request</p>