When the NodeAttrDNSSubdomainResolve capability is present, enable
wildcard certificate issuance to cover all single-level subdomains
of a node's CertDomain.
Without the capability, only exact CertDomain matches are allowed,
so node.ts.net yields a cert for node.ts.net. With the capability,
we now generate wildcard certificates. Wildcard certs include both
the wildcard and base domain in their SANs, and ACME authorization
requests both identifiers. The cert filenames are kept still based
on the base domain with the wildcard prefix stripped, so we aren't
creating separate files. DNS challenges still used the base domain
The checkCertDomain function is replaced by resolveCertDomain that
both validates and returns the appropriate cert domain to request.
Name validation is now moved earlier into GetCertPEMWithValidity()
Fixes#1196
Signed-off-by: Fernando Serboncini <fserb@tailscale.com>
5edfa6f9a8