I'm looking for a program that is going to connect to all my SSL sites, and report back a problem if the cert is within 30 days of expiration. It is easy enough to write a client that will fail after the cert has expired, but I want one that will warn me ahead of time. And I don't want to mess with the system clock or something like that.
It shouldn't be a big program, I may just write it myself.
define command {
command_name check_certificate
command_line $USER1$/check_http -H $ARG1$ -p $ARG2$ -4 -S -C 21 -t 20 --sni
}
is totally free, superfast and checks your TLS settings too (it's my baby)
Also my employer (well, until the end of this week) Kynd does this as part of its broader "Check cyber-security stuff" offering for non-technical people. https://www.kynd.io/