title: github oauth with multiple domains
body: <p>i am running an application that runs on several subdomains usergroupXYZ.onruby.de and also supports arbitrary domains as aliases. so you can access the domain via yourusergroup.onruby.de or via customdomain.de.</p>
  
  <p>the app provides logins via twitter oauth and github oauth2.</p>
  
  <p>the problem is, that i did not find a way to support github auth via custom domains. i always get <code>redirect_uri_mismatch</code> errors from github.</p>
  
  <p>the twitter auth does not have a problem with redirecting to a different domain.</p>
  
  <p>does anyone have a solution to this problem other than creating a github application token for each custom domain?</p>