[pjf]

https://bgpipe.org/

I'm working on a man in the middle proxy for BGP, which can fix and inspect routing sessions on the fly. Like a firewall for the BGP control plane.

[AquiGorka]

Some time ago I was building a mitm proxy myself, then I found out about: https://www.mitmproxy.org/ Maybe you already had it in your radar

[KomoD]

That's for HTTP/S and related, as parent said his is for BGP which is a completely different protocol