[Feature Request] add support for https proxy (frpc -> httpsProxy -> frps)

[ofirc]

Describe the feature request

I saw both in the README.md, the frpc.toml sample, and the golib code itself (link1, link2) that we only support: socks5, http and ntlm:

var supportedDialProxyTypes = []string{"socks5", "http", "ntlm"}

But what if I have an https proxy, e.g. https://my.proxy.server.com:8888 rather than http://my.proxy.server.com:8888?
Was wondering why isn't it supported and what would it take to support an HTTPS proxy?
For the sake of clarity, I don't care about MitM (man-in-the-middle) proxies, I'm talking about a scenario where the frpc (frp client) connects to frps (frp server) through a proxy with an https:// protocol scheme.

I'm guessing that from the user's perspective we'd need to (1) pass a custom CA (as most likely it's a local proxy with a private PKI), (2) add TLS handshake support to golib and the rest should be the same, i.e. pass a CONNECT to frps over that established connection.

I know that it might not make a lot of sense to everyone to actually use an https proxy, but nevertheless wondering what's the dev effort / design considerations that were led to not supporting it.

Thanks!
Ofir

Describe alternatives you've considered

No response

Affected area

• Docs
• Installation
• Performance and Scalability
• Security
• User Experience
• Test and Release
• Developer Infrastructure
• Client Plugin
• Server Plugin
• Extensions
• Others

[fatedier]

I personally haven’t used an HTTPS proxy much myself, but if the behavior is similar to that of an HTTP proxy, we should be able to support it. Would you be able to help modify the code and test/verify it?

[ofirc]

Yes, I will update this issue once I change the code and test it.
Thanks!

[xqzr]

if the behavior is similar to that of an HTTP proxy, we should be able to support it.

HTTPS 代理在 HTTP/1.1 版本下，只是添加了 TLS，即 HTTP+TLS