title: How do you restrict permissions to a specific action with guardian and phoenix
body: <p>I have set up guardian to encode specific permissions in the token, however, I would like to restrict this in my <code>UserController</code> to just require it on specific actions (<code>[:index, :show, :edit, :update, :delete]</code>). I use the following line at the top of the controller to require the <code>admin: [:cms]</code> permission for the entire controller:</p>
  
  <p><code>plug Guardian.Plug.EnsurePermissions, handler: Ay.Guardian.ErrorHandler, admin: [:cms]</code></p>
  
  <p>This works fine but I would like to add a guard like clause to this (e.g. <code>when action in [:index, :show, :edit, :update, :delete]</code>) but I can't seem to get this to work the way I want to. </p>
  
  <p>I realize I can easily check the claims in each action but because of the large amount of controllers I would like a more generic approach. </p>