Every .dk domain that delegates its _acme-challenge name to c5bb19f4-c5e5-46be-b0f5-5b10096cffc4.auth.acme-challenge.dk. Such CNAMEs hand DNS-01 certificate validation to a shared service, so this list shows who issues TLS certificates through it. Data comes from our own scanners, which re-resolve every .dk domain in the zone roughly once a week.