Certificate Authority Authorization (CAA) is a DNS based security protocol that allows domain owners to define which entities are allowed to generate certificates.

DNS Certificate Authority Authorization (CAA)

You can set CAA records on your main domain, or at any depth of subdomain. For instance, if you had www.community.example.com, … CAs will check each version, from left to right, and stop as soon as they see any CAA record. … Most people who add CAA records will want to add them to their registered domain (example.com) so that they apply to all subdomains. …

example.com IN CAA 0 issue letsencrypt.org

The DNS hosting service should have a dedicate CAA record type which allows to select between issue (only specific hostnames), wildissue (only wildcard hostnames), and iodef (report violations).

To check the CAA record, use host or dig:

$ host -t CAA litux.org
litux.org has CAA record 0 issue "letsencrypt.org"
litux.org has CAA record 0 iodef "mailto:…@litux.org"
$ dig +short -t CAA litux.org
0 issue "letsencrypt.org"
0 iodef "mailto:…@litux.org"