title: Controlling access to docker registry with Sonatype nexus
body: <p>In our current setup we are do proxy to entire docker hub to pull the images, but what we want is limit this proxy to only official indexes like ubuntu, apache etc. 
  During configuration of repository there was this option to set <code>custom index</code> for the repository, so my two questions are :</p>
  
  <ul>
  <li>With this <code>custom index</code> option will I be able to achieve what I explained above?</li>
  <li>If yes, then from where I should get the URL for custom index. so far I tried using <code>https://hub.docker.com/_/centos/</code> for centos but it didn't worked.</li>
  </ul>
  
  <p>Please suggest how to go about this.</p>