title: Django auth system: adding user to group via "invites"
body: <p>I want to use the Django default auth system to manage users and groups. Is there an existing Django app/module that adds users to groups by invites? I.e. some existing user of the group sends an invite with a secret key in a URL, and another user that clicks on the URL joins the group.</p>
  
  <p>I can write one, but figured I ask before doing that.</p>
  
  <p>Thanks.</p>