Is it possible to monitor TLS connections?

Hi, at the moment I have the following scenario:

gRPC server <------ Traefik <--- TLS ---- gRPC clients

Basically I'm using Traefik to terminate long-lived TLS connections which I'd like to monitor in order to know exactly when a specific client has a connections established. Clients are identified by info in their TLS cert that is then used as metric labels.

With Prometheus it would look something like this.
Connection is up:
tcp_conn_status{client_id="..."} 1
Connection goes down
tcp_conn_status{client_id="..."} 0

I did some tests with a custom HTTP middleware but that didn't work and, custom TCP middleware are not possible yet if I'm not mistaken.

Is this possible to do with Traefik?