Every .dk domain that delegates its _acme-challenge name to 61c3080f-c780-4580-ba72-9c7b63cc51dd.acme-auth.itcn.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.