I'm looking after some RHEL6 servers and trying to set them up to use an internal PyPi server (proxied by Nexus 3).
The problem is that our internal PyPi server is one of several SSL VHosts on the same Nginx server, and Python 2.6 is not SNI compatible; thus, easy_install fails because it's trying to download from the wrong Vhost URL and pip fails with SNIMissingWarning and InsecurePlatformWarning.
I looked at the advice on https://urllib3.readthedocs.io/en/latest/advanced-usage.html#ssl-warnings but it seems this is a workaround for your own scripts; it doesn't address problems in Python itself. I installed urllib3 and the associated packages anyway, and the problem remains.
[firstname.lastname@example.org ~]# pip install --index https://nexus3.internal/repository/pypi-proxy/simple twine DEPRECATION: Python 2.6 is no longer supported by the Python core team, please upgrade your Python. A future version of pip will drop support for Python 2.6 Collecting twine /usr/lib/python2.6/site-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:318: SNIMissingWarning: An HTTPS request has been made, but the SNI (Subject Name Indication) extension to TLS is not available on this platform. This may cause the server to present an incorrect TLS certificate, which can cause validation failures. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#snimissingwarning. SNIMissingWarning /usr/lib/python2.6/site-packages/pip/_vendor/requests/packages/urllib3/util/ssl_.py:122: InsecurePlatformWarning: A true SSLContext object is not available. This prevents urllib3 from configuring SSL appropriately and may cause certain SSL connections to fail. You can upgrade to a newer version of Python to solve this. For more information, see https://urllib3.readthedocs.io/en/latest/security.html#insecureplatformwarning. InsecurePlatformWarning Could not fetch URL https://nexus3.internal/repository/pypi-proxy/simple/twine/: There was a problem confirming the ssl certificate: [Errno 1] _ssl.c:490: error:14090086:SSL routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed - skipping Could not find a version that satisfies the requirement twine (from versions: ) No matching distribution found for twine