title: SSL error while uploading python package to custom registry using twine
body: <p>When trying to upload a python custom package to our internal registry its failing with the following error.</p>
  
  <pre><code> urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='custom-nexus.com’, port=443): Max retries exceeded with url: /repository/pypi-internal/ (Caused by SSLError(SSLError("bad handshake: Error([('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')],)",),))
  </code></pre>
  
  <p>But the same url works fine when accessed through curl. Using curl -v option found that the ca-bundle used was in the location /etc/pki/tls/certs/ca-bundle.crt</p>
  
  <p>So tried providing this in the twine upload command using the --cert option. But then also its not working and failing with the same error.</p>
  
  <pre><code>twine upload --config-file .pypirc   --cert /etc/pki/tls/certs/ca-bundle.crt  -r pypi dist/*
  </code></pre>
  
  <p>Python version used is 3.6. Please find below the list of library versions. </p>
  
  <pre><code>certifi==2020.4.5
  setuptools==46.1.3
  wheel==0.34.2
  twine==3.1.1
  pyOpenSSL==19.1.0
  </code></pre>