Implements missing HTTPS proxy functionality

[seans3]

What type of PR is this? (check all applicable)

• Feature

Description

• Implements missing HTTPS Proxy functionality.
• Adds both client/proxy/server tests and unit tests.

Related Tickets & Documents

• Closes [feature] Support for proxying websocket through https proxy #739
• Closes Is https not supported?  #794

Added/updated tests?

• Yes

Run verifications and test

$ go test -race -cover
PASS
coverage: 84.3% of statements
ok  	github.com/gorilla/websocket	4.103s

[seans3]

/cc @adrianosela

[seans3]

/assign @liggitt
/assign @aojea

[adrianosela]

Thanks for this @seans3 🚀

[aojea]

IIUIC the same certificate is used for both the proxy and the backend, don't we need to handle the case when both are different? what happens if the proxy requires a different certificate than the backend?

EDIT

I see, the TLSConfig can be used for that, also @seans3 sent me this https://github.com/adrianosela/https-proxy/tree/main?tab=readme-ov-file#https-proxy

[seans3]

IIUIC the same certificate is used for both the proxy and the backend, don't we need to handle the case when both are different? what happens if the proxy requires a different certificate than the backend?

The client is responsible for configuring the root CA certificates. The client TLS config contains a cert pool, which can contain multiple root CA certificates. So for TLS to the proxy and the upstream, the TLS config root CA cert pool must contain CA's which have signed both the proxy and the upstream.

[134130]

This PR also closes #950