What is the best practice for certificate management on an IOT device (bare metal microcontroller with GSM modem that communicates to a secured MQTT broker)?
Looking at Let's Encrypt certbot, they have 90 day expiry, then the certs should be updated. Should the certs also be sent via the existing secured MQTT connection when it is time for update? How if the device was turned off for a long time and when opened, it is already past the cert expiry? I learned that self-signed certificate is a bad idea however using it will greatly simplify the certificate management as the expiry date could be lengthen to many years.
I am wondering how the wifi cameras handle their certificate management.