How can I check the expiration date of a Certificate Keychain from terminal?

Hello, I am writing a bash script to alert me when my corporate certificates are about to expire. How can I check the expiration date of a certificate in keychain? I'm running Mac OS 10.6.8 on a newer MacBook pro with full admin rights.

Specifically I will be checking three certs: a Root Authority, Issuing Authority, and a user cert (Identity).

I was exploring the Security and Openssl command line tools. But I can't seem to get the info I need.

Any recommendations would be appreciated.

Thank you!