e.g. contains control characters, Punycode conversion fails
There are quite simply too many certs with bogus DNS labels out in the wild,
and it just doesn't make sense to bother every .com domain holder because
GoDaddy signed a cert with a DNS name like "www. just4funpartyrentals.com"
It is highly unlikely any validator will ever match that DNS name.
All certificates are now parsed with a special, extremely
lax parser that extracts only the DNS names. Only if the
DNS names match the domains we're interested in will we attempt
to parse the cert with the real X509 parser. This ensures that
we won't miss a very badly encoded certificate that has been
issued for a monitored domain.
As of the time of commit, the lax parser is able to process every
logged certificate in the known logs.
Now that we save all certs by default, we want to prevent people
from accidentally monitoring all domains, which could lead to MASSIVE
disk usage.
"." is used because it denotes the root zone in DNS.
Andrew Ayer