Every .dk domain that delegates its _acme-challenge name to 51a61da5-bfc0-474d-95ba-c5222c541202.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.