Notify users when Yubikey Cert is about to expire

Hello,

I want users to get notified "popup" 1 month before Yubikey Cert will expire.

Note: Cert is in the plugged device not in Keychain.

Am using EA to show expiry date: 

#!/bin/sh

Expire=$(/Applications/YubiKey\\ Manager.app/Contents/MacOS/ykman piv info | grep after | awk '{print $3}')

echo "<result>$Expire</result>"

Any idea?