title: pip install private repo extras EnvironmentError
body: <p>I have a custom package in a private repo. I'm able to install it with:</p>
  <pre><code>pip install &quot;git+https://myserver.com/subfolders/my_repo.git#egg=my_package&amp;subdirectory=my_package&quot;
  </code></pre>
  <p>This works fine. I've added two extra dependencies in <code>setup.py</code>:</p>
  <pre><code>extras_require = {
      'depa' : [&quot;another_package @ git+https://myserver.com/subfolders/my_repo.git#egg=another_package&amp;subdirectory=another_package&quot;],
      'depb' : [&quot;some_other_package @ git+https://myserver.com/subfolders/my_repo.git#egg=some_other_package&amp;subdirectory=some_other_package&quot;],
  }
  </code></pre>
  <p>I can install the extra dependencies with:</p>
  <pre><code>pip install -e .[depa,depb]
  </code></pre>
  <p>However, when I try to install using the package's URL, it fails:</p>
  <pre><code>pip install &quot;git+https://myserver.com/subfolders/my_repo.git#egg=my_package&amp;subdirectory=my_package&quot;[depa,depb]
  Collecting my_package
    Cloning https://myserver.com/subfolders/my_repo.git to c:\users\my_user\appdata\local\temp\pip-install-j0o9f85u\my_package
      ERROR: Error [WinError 267] The directory name is invalid while executing command python setup.py egg_info
  ERROR: Could not install packages due to an EnvironmentError: [WinError 267] The directory name is invalid
  </code></pre>
  <p>Is there a way to use pip to install the package from a private URL while at the same time specifying the extras?</p>
  <p>Thanks!!</p>