3. Relevant Resource Record Set

Before issuing a certificate, a compliant CA MUST check for publication of a Relevant RRset. If such an RRset exists, a CA MUST NOT issue a certificate unless the CA determines that either (1) the certificate request is consistent with the applicable CAA RRset or (2) an exception specified in the relevant CP or CPS applies. If the Relevant RRset for an FQDN or Wildcard Domain Name contains no Property Tags that restrict issuance (for instance, if it contains only iodef Property Tags or only Property Tags unrecognized by the CA), CAA does not restrict issuance.

A certificate request MAY specify more than one FQDN and MAY specify Wildcard Domain Names. Issuers MUST verify authorization for all the FQDNs and Wildcard Domain Names specified in the request.

The search for a CAA RRset climbs the DNS name tree from the specified label up to, but not including, the DNS root "." until a CAA RRset is found.

Given a request for a specific FQDN X or a request for a Wildcard Domain Name *.X, the Relevant RRset RelevantCAASet(X) is determined as follows (in pseudocode):

Let CAA(X) be the RRset returned by performing a CAA record query
for the FQDN X, according to the lookup algorithm specified in
Section 4.3.2 of [RFC1034] (in particular, chasing aliases). Let
Parent(X) be the FQDN produced by removing the leftmost label of
X.

RelevantCAASet(domain):
  while domain is not ".":
    if CAA(domain) is not Empty:
      return CAA(domain)
    domain = Parent(domain)
  return Empty

For example, processing CAA for the FQDN "X.Y.Z" where there are
no CAA records at any level in the tree RelevantCAASet would have
the following steps:

CAA("X.Y.Z.") = Empty; domain = Parent("X.Y.Z.") = "Y.Z."
CAA("Y.Z.")   = Empty; domain = Parent("Y.Z.")   = "Z."
CAA("Z.")     = Empty; domain = Parent("Z.")     = "."
return Empty

Processing CAA for the FQDN "A.B.C" where there is a CAA record
"issue example.com" at "B.C" would terminate early upon finding
the CAA record:

CAA("A.B.C.") = Empty; domain = Parent("A.B.C.") = "B.C."
CAA("B.C.")   = "issue example.com"
return "issue example.com"

3. Relevant Resource Record Set​

3. Relevant Resource Record Set