Access SYN using TCP server type plugin

Regarding this plugin: https://caddyserver.com/v1/docs/net,
Is it possible to get the handshake data of the TCP session? For example the SYN packet and be able to access things like tcp.window_size, tcp.options, etc.?

Or is this plugin used only to inspect\proxy the TCP data?

In case it’s not possible to access these stuff from the plugin, would it be possible through some library of Caddy or perhaps even by modifying a GO library? It looks to me like not, since the src/net/ uses an API that gives it an existing TCP socket, and doesn’t deal with the handshake itself, please correct me if I’m wrong

Even a partial reply to one of my sub questions (plugin, Caddy libraries or GO libraries) would be helpful, thanks!