PROD Support for RFC8657 CAA constraints for accountURI and validationmethods

[Osiris]

@MikeMcQ

Good question on cached validations. LE should make that clear in their FAQ about them. I now wonder what happens if even the CAA issue value were changed during the cached period. Would LE check CAA or fully rely on cache?

CAA RR are cached MUCH shorter than valide authz (8 hours instead of 30 days). In fact, the lack of maintaining this shorter cache time in certain situations has lead to a quite serious incident: 2020.02.29 CAA Rechecking Bug