title: Using pip with two --extra-index-url arguments that both point to the same domain
body: <p>We use our own python package index at my office, and we're trying to add a new one. When I try to specify both indices at the same time, I get prompted to log in, but if I use only one at a time I don't.</p>
  
  <p>For example:</p>
  
  <pre><code>$ pip install --user --upgrade \
      --extra-index-url https://&lt;api token&gt;:@packagecloud.io/2rs2ts/oldrepo/pypi/simple \
      --extra-index-url https://&lt;other api token&gt;:@packagecloud.io/2rs2ts/newrepo/pypi/simple \
      mypackage
  Collecting mypackage
  User for packagecloud.io:
  </code></pre>
  
  <p>But if I specify just one of either of those <code>--extra-index-url</code> arguments then I download my package just fine.</p>
  
  <p>I'm 99% certain that I am passing the arguments correctly, since <a href="https://github.com/pypa/pip/blob/master/pip/cmdoptions.py#L228-L238" rel="noreferrer">it's specified with an <code>append</code> action in the source</a>. So I think the problem is that both of these index URLs are from <code>packagecloud.io</code>... but I could be wrong. Either way, how can I use both of my repos?</p>