I tested manually that it works, steps

1. Run httpbin on localhost 8443

   go run ./cmd/forwarder/ test httpbin --protocol https --address 127.0.0.1:8443 --api-address

2. Run proxy with MITM

   SSLKEYLOGFILE=/tmp/keys go run ./cmd/forwarder/ run --mitm --insecure --proxy-localhost allow

3. Run tshark

   tshark -i lo0 -f "tcp port 8443" -Y "http" -o "tls.keylog_file:/tmp/keys"

4. Run curl

   curl -k -v -x localhost:3128 https://localhost:8443/status/200

tshark should report HTTP payload

Capturing on 'Loopback: lo0'
   13   0.005530    127.0.0.1 → 127.0.0.1    HTTP 363 GET /status/200 HTTP/1.1
   15   0.006096    127.0.0.1 → 127.0.0.1    HTTP 153 HTTP/1.1 200 OK

Fixes #579