Add support for SSLKEYLOGFILE

[Nicoretti]

Hi @ all,

Thanks for maintaining and providing this library, appreciate it! 👍

Recently I have been debugging some protocol on top of websockets. The client I have been debugging
was using this library for it's websocket communication. This is why I stumbled upon the fact, that
the SSLKEYLOGFILE will be not supported in all cases when using this library.
I am aware that one always can pass a completely custom SSLContext, but I am not 100% sure if that should
be required here. Happy to get some feedback on this from the maintainers.

Summary

Python >= 3.8 supports SSLKEYLOGFILE for debugging, see here.
Which is a very helpful feature for debugging SSL/TLS connections without disabling it.

What is this good for?

The SSLKEYLOGFILE can be used to dump TLS session keys to a file which enables the user to decrypt the TLS traffic. This has the "advantage" that an actual TLS secured connection can be debugged, rather than a connection
where TLS is disabled. In some scenarios, connecting without TLS may not even be possible.

See also

• CURL-SSLKEYLOGFILE
• Wireshark - tls-decryption
• Python - SSLKEYLOGFILE

I hope the provided information is sufficient.

best
Nico

[engn33r]

Thanks for the helpful PR!