title: Filtering users who are able to sign in with Devise
body: <p>I have a Rails app using Devise for authentication. Users belong to Dealers and I want to prevent users who belong to disabled dealers from being able to sign in.</p>
  
  <p>Is there a straightforward way to <strong>extend Devise's authentication finder</strong> so that it will not include users from deleted dealers? Perhaps using a named scope on User?</p>
  
  <p>Cheers</p>
  
  <p>Tristan</p>