:gen_event handler that reloads TLS certificates on SIGHUP.
What problem this solves
Deployment hooks (systemd, xturn-deploy-certs.sh) can signal the running
node to pick up renewed PEM files immediately instead of waiting for the
poll interval. This handler invokes Certs.reload/0 when the BEAM receives
:sighup.
Internal: registered on :erl_signal_server by
Certs.SignalHandler.Registrar at boot.
RFCs
No STUN/TURN RFC applies. Operations concern for TLS/DTLS certificates used with TURNS (see RFC 8656 for TURN over TLS/DTLS transports).