title: Customize Error Message When Permission Check Fails
body: <p>The DRF documentation provides clear instructions on <a href="http://www.django-rest-framework.org/api-guide/permissions/#custom-permissions" rel="noreferrer">how to create a custom permission</a>, offering the following code sample:</p>
  
  <pre><code>from rest_framework import permissions
  
  class BlacklistPermission(permissions.BasePermission):
  """
  Global permission check for blacklisted IPs.
  """
  
      def has_permission(self, request, view):
          ip_addr = request.META['REMOTE_ADDR']
          blacklisted = Blacklist.objects.filter(ip_addr=ip_addr).exists()
          return not blacklisted
  </code></pre>
  
  <p>By default this gives the following response when the permission check function return <code>False</code>.</p>
  
  <blockquote>
    <p>HTTP 403 FORBIDDEN<br>
    Content-Type: application/json<br>
    Vary: Accept<br>
    Allow: GET, POST, HEAD, OPTIONS  </p>
    
    <p>{
        "detail": "You do not have permission to perform this action."
    }</p>
  </blockquote>
  
  <p>I would like to change the "detail" section above, offering a more developer-friendly error message. How could I do this, ensuring the message is presented each time the permission check fails?</p>