CAA check library in Golang. Using https://github.com/miekg/dns for the DNS lookups.
Initial CAA checker commit. Many things to do...
Here some DNS response codes, maybe I have to map them later.
0 = NOERR, no error 1 = FORMERR, format error (unable to understand the query) 2 = SERVFAIL, name server problem 3 = NXDOMAIN, domain name does not exist 4 = NOTIMPL, not implemented 5 = REFUSED (e.g., refused zone transfer requests)
Some CA's seem to check different then others. Not all resolving nameservers are giving the same answers.