In the FAQ page,
I successfully renewed a certificate but validation didn’t happen
this time - how is that possible?
Once you successfully complete the challenges for a domain,
the resulting authorization is cached for your account to use again
later. Cached authorizations last for 30 days from the time of
validation. If the certificate you requested has all of the necessary
authorizations cached then validation will not happen again until the
relevant cached authorizations expire.
Is this quote derived from the service specification of Let’s encrypt?
Or, is there any reference such as IETF draft describing about this?
(As long as I looked up, I couldn’t find other helpful references.)