title: 30 char limit error when logging into django site with email and password
body: <p>I have added a custom backend to allow a user to log in with a username or email in addition to password. It works fine except when the email is longer than 30 characters. The form error I get is: </p>
  
  <pre><code>"Ensure this value has at most 30 characters (it has 35)."
  </code></pre>
  
  <p>In one my my apps' urls.py file I've overridden the max_length of the username field like this:</p>
  
  <pre><code>from django.contrib.auth.forms import AuthenticationForm
  AuthenticationForm.base_fields['username'].max_length = 75
  </code></pre>
  
  <p>I've even tried the class_prepared signal technique described here:</p>
  
  <pre><code>http://stackoverflow.com/questions/2610088/can-djangos-auth-user-username-be-varchar75-how-could-that-be-done/2613385#2613385
  </code></pre>
  
  <p>I'm not sure where I'm going wrong here and I appreciate the help. </p>