HTTPS proxy can cause confusing 'Error: write EPROTO 8669745856...' error

[BogdanCln]

Hello and thanks for taking your time to read this!

The issue I'm facing is that sometimes the proxy responds with an error status code to the CONNECT request which is not handled.
Currently, global-agent considers that once a response for the CONNECT request is received, it is fine to start the TLS handshake. That will result in a confusing error if the proxy refuses the connection:
Error: write EPROTO 8669745856:error:1408F10B:SSL routines:ssl3_get_record:wrong version number:../deps/openssl/openssl/ssl/record/ssl3_record.c:332:.
Two common cases when this happens are wrong authentication and proxy access filter declining the request. In both cases, the proxy will respond with an error status code (>=400) to the CONNECT request.

I created a PR for this: #61

More details and replication guide are included there.

[NPhMKgbDNy1M]

I have the same problem!