title: Docker: How to authenticate for docker push?
body: <p>Hi i'm trying <code>docker push</code></p>
  
  <pre><code>[docker-simple-httpserver]# docker push myregistry/simplehttpserver:latest
  The push refers to a repository [myregistry/simplehttpserver] (len: 1)
  Sending image list
  FATA[0000] Error: Status 403 trying to push repository simplehttpserver: "{\"error\": \"Unauthorized updating repository images\"}" 
  </code></pre>
  
  <p>is there a way for me to specify the <code>username</code> and <code>password</code> on <code>docker push</code> command?</p>