Client Certificate Expiration

[Kling]

Right now, I see that ColdFusion offers the following CGI variables for Client Certificates:
CERT_COOKIE
CERT_ISSUER
CERT_SERIALNUMBER
CERT_SUBJECT
CLIENT_CERT_ENCODED

It would be nice to warn people that their certificates are about to expire so they can reapply.
I would like to see it like this site can:
https://infosec.navy.mil/cgi-bin/testmypki.cgi

Maybe it's somehow encoded in CLIENT_CERT_ENCODED or CERT_COOKIE (and there's an easy way to decode it)
Or, worst case scenerio, I could have an ASP page pass it if I had to.
Thanks!

[Kling]

OK, I've made some progress...
I found one thing that ASP can do that CF can't: Read when a Certificate Expires.
In ASP, I can do this: