Every .dk domain that delegates its _acme-challenge name to f7c2267d-e406-4edc-bf23-c4e965c14e1d.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.