Provide TlsRef details to HTTP/2 requests

[jaw-sh]

What is the problem your feature solves, or the need it fulfills?

TLS information can be valuable for security purposes. Cloudflare implements JA4 fingerprinting in its own security services.

https://blog.foxio.io/ja4+-network-fingerprinting
https://blog.cloudflare.com/ja4-signals/

Currently Pingora appears to discard TLS information on HTTP/2 requests. It is very possible to make a JA4 fingerprint inside request_filter if the request is HTTP/1. HTTP/2 does not provide the same information.

pingora::http::client.rs

    /// Get the reference of the [Stream] that this HTTP/1 session is operating upon.
    /// None if the HTTP session is over H2
    pub fn stream(&self) -> Option<&Stream> {
        match self {
            Self::H1(s) => Some(s.stream()),
            Self::H2(_) => None,
            Self::Custom(_) => None,
        }
    }

Describe the solution you'd like

Please provide some way to access TlsRef for HTTP/2 requests via .stream(), same as HTTP/1.

If Pingora is adverse to creating a lookup table for SSL information, please provide callbacks with useful information (SocketAddr?) that would allow the developer to create his own.

Describe alternatives you've considered

Accessing this information with HTTP2 has been very frustrating. The underlying TLS information is discarded before the first request cycle begins, so there is no promise request_filter is ever called as HTTP/1.1 before movnig to HTTP/2. The developer has no appropriate window to begin tracking this information.

I had the idea to try and record the SocketAddr being used for that HTTP2 session using set_client_hello_callback, but unfortunately OpenSSL does not provide any information on the client ip or ephemeral port being used for that session. I attempted to look in C-land for ways to associate the handshake with subsequent requests but it is not obvious and I really don't know what I'm doing there. I can JA4 fingerprint in this callback, but I cannot store it in any meaningful way.

[tqlab]

#723