Change the SetCommonName flag, introduced in #6706, to
RequireCommonName. Rather than having the flag control both whether or
not a name is hoisted from the SANs into the CN *and* whether or not the
CA is willing to issue certs with no CN, this updated flag now only
controls the latter. By default, the new flag is true, and continues our
current behavior of failing issuance if we cannot set a CN in the cert.
When the flag is set to false, then we are willing to issue certificates
for which the CSR contains no CN and there is no SAN short enough to be
hoisted into the CN field.
When we have rolled out this change, we can move on to the next flag in
this series: HoistCommonName, which will control whether or not a SAN is
hoisted at all, effectively giving the CSRs (and therefore the clients)
full control over whether their certificate contains a SAN.
This change is safe because no environment explicitly sets the
SetCommonName flag to false yet.
Fixes#5112
6d6f3632da