
github.com/elazarl/goproxy does not properly handle upgrades over HTTP
proxy. The problem is this misinterpretation:
6691876326/vendor/github.com/elazarl/goproxy/proxy.go (L89-L95)
These should be stripped but recalculated then added back:
https://cs.opensource.google/go/go/+/refs/tags/go1.19.3:src/net/http/httputil/reverseproxy.go;l=292-297;drc=f6d844510d5f1e3b3098eba255d9b633d45eac3b
Let's just stop using goproxy, and use the stdlib instead. The
functionality we need is straightforward to implement and goproxy is
overkill.