title: How can I install extras with `pip install git+ssh`?
body: <p>I have an internal Python package which I install for <code>tox</code> with</p>
  
  <pre><code>pip install git+ssh://git@bitbucket.org/org/repo.git
  </code></pre>
  
  <p>This works.</p>
  
  <p>What does not work is to install the extra <code>server</code>. </p>
  
  <h2>What I tried</h2>
  
  <pre><code>pip install git+ssh://git@bitbucket.org/org/repo.git[server]`
  </code></pre>
  
  <p>git clone failed with error code 128 (couldn't clone)</p>
  
  <pre><code>pip install git+ssh://git@bitbucket.org/org/repo.git [server]
  </code></pre>
  
  <p>Cloning works, <code>Invalid requirement: '[server]'</code> (a parsing exception</p>
  
  <pre><code>pip install -e git+ssh://git@bitbucket.org/org/repo#egg=repo[server]
  </code></pre>
  
  <blockquote>
    <p>Could not detect requirement name for 'git+ssh://git@bitbucket.org/org/repo.git', please specify one with #egg=your_package_name</p>
  </blockquote>
  
  <hr>
  
  <p>I think I might be affected by <a href="https://github.com/tox-dev/tox/issues/181" rel="noreferrer">this bug</a>: <a href="https://stackoverflow.com/q/52717761/562769">How can I install extras with `pip install git+ssh`?</a></p>
  
  <p>My (simplified) <code>tox.ini</code>:</p>
  
  <pre><code>[tox]
  skipsdist = True
  envlist = begin,py35,py36,end
  
  [testenv]
  commands =
      pip install -e git+ssh://git@bitbucket.org/org/repo#egg=repo[server]
  </code></pre>