title: ActiveAdmin role for mass assignment
body: <p>In my models I have defined different roles for mass assignment. Some fields are <code>attr_accessible :as =&gt; :default</code>. Other fields are <code>attr_accessible :as =&gt; [:default, :admin]</code>.</p>
  
  <p>How can I allow ActiveAdmin to be able to update attributes as an admin role?</p>