title: stop field to being update in cakephp
body: <p>In my cake PHP application, I have a edit form where "email" field is readonly that means user can not update it.
  NOw if I think according to security point of view, user can update the field by 'firebug' or some other browser plugins.</p>
  
  <p>I am using <code>$this-&gt;User-&gt;save($this-&gt;data)</code> to save the updated data. By this function Email can be also be updated.</p>
  
  <p>Do we have any way in cake php so that I can prevent this field to be update, like by passing here a argument or something like this?</p>