title: Overriding authenticate method - Django admin
body: <p>I'm trying to figure out how to enhance the authenticate method with additional functionality.</p>
  
  <p>e.g. </p>
  
  <ul>
  <li>Expiring passwords </li>
  <li>special password formats </li>
  <li>length requirements </li>
  <li>etc...</li>
  </ul>
  
  <p><strong>It is pretty straight forward for the site's frontend, but what about the admin panel?</strong></p>
  
  <hr>
  
  <p>I reckon that I should override the User's Manager object, as authenticate probably resides there. This is quite a tough one to figure out I think.</p>
  
  <p>Thanks in advance! :)</p>