sslderp
This is a simple utility to report things about remotely hosted SSL certs.
Presently, it will make a HTTPS connection to a given server and will report the number of days remaning until that certificate expires. This is also why it is named sslderp, as in - "OH, DERP, MY CERT EXPIRED!"
Example usage: sslderp --target www.example.org --nagios
If you pass -n or --nagios to the utility, it will return Nagios/Icinga- compatible exit codes if the certificate is close to expiry. <30 days will generate a WARNING (exit 1), <15 days will generate a CRITICAL (exit 2) and anything >30 days will return a clean 0.