Ugh. It’s happening…
For users of Python 2.7.{0...8}
Upgrading to the last Python 2.7 release is an option.
However, note that Python 2.7 series itself is now End of Life and support in pip was dropped with version 21.0.
For users of Python 2.6.x and lower:
Neither the Python core developers, or pip maintainers support Python 2.6 and below.
If someone is aware of a work around for this issue (SNI support specifically) they are welcome to share it here for others.
There is no recommended solution from the PyPI team.