title: User field missing in system.profile collection when connecting with Mongos
body: <p>We have a MongoDB cluster and clients connecting to it through a Mongos instance. The individual mongo(s) in the cluster are all running with <code>--auth</code>, and the Mongo use a <code>--keyfile</code> when communicating with them. We are profiling slow queries but are not getting the user names on queries that go through Mongo. </p>
  
  <p>To make it clearer:</p>
  
  <ol>
  <li><p>If I connect directly to one of the Mongo, authenticate, and run a query, then I can look in the <code>system.profile</code> collection afterwards, and the <code>user</code> field will be populated with my username.</p></li>
  <li><p>If I connect through mongos, authenticate, and run a query, then the system.profile collection contains profiling info about the query, but the user field is blank.</p></li>
  </ol>
  
  <p>The authentication is required, I can't run a query through Mongo without authenticating first, but the user name just doesn't seem to be included in the profiling info, and we'd really like to be able to see it.</p>
  
  <p>Any ideas? Any alterations I can make to our  configuration?</p>