We have a network telemetry extension that wants to use some metadata passed as a response header for CONNECT tunneling initiated by tcp_proxy. We want an ability to expose those headers to network extensions beyond just checking for 200. I have a couple of ideas:

• copy headers to the downstream L4 filter state; maybe require explicit names and mapping;
• copy headers as dynamic metadata to the downstream L4 filter state;
• create a mechanism to make upstream L7 filters somehow access downstream L4 stream info;
• rewrite the telemetry to be an upstream L7 filter instead for CONNECT.

Thoughts? @alyssawilk