mod_client_certs: do not crash on plain sockets In some situations (e.g., reverse-proxied websocket), non-TLS sockets can be marked as secure, causing mod_client_certs to call the undefined method getpeercertificate and crash.

---
summary: Log a message once per minute
...

This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.