SDK 2.0.1 checks the server host name in TWO places: Session.OpenAsync (after
the chain is trusted) and DefaultSessionFactory.CreateChannelAsync, against the
certificate in the GetEndpoints reply and before any security-mode test. opc-plc
sends a certificate on its None endpoint, so `connect -u
opc.tcp://10.100.0.35:50000 --validate-host-name` was refused on an
unauthenticated channel, where a host check proves nothing.
All three call sites now pass checkDomain only when the selected endpoint's
SecurityMode != None: OpcUaEndpointSelection.CheckDomainFor for the driver
(OpenSessionOnEndpointAsync, so the failover sweep too) and the AdminUI browser;
the same expression in Client.Shared ConnectToEndpointAsync (shared by
failover). New live tests: driver None + flag on vs :50000 reads; browser None +
flag on vs the NAT fixture browses; the secure + flag refusals still hold.
Docs: name both check sites; a zone-qualified IPv6 host never matches (FindDomain
compares the zone too), so link-local needs validateServerHostName=false; the
match is loose (first label alone, subject DC= parts count, no wildcards), which
caveats the CA recommendation.
#816 finding: the SDK checks that the server certificate names the host only
when a session is created with checkDomain:true. The driver, the AdminUI
browser and Client.Shared all called the 8-argument
DefaultSessionFactory.CreateAsync, which forwards checkDomain:false — so no
host-name check ever ran (why a trusted NAT cert for *.invalid browsed fine
over an IP in #813). When enabled the SDK (Session.OpenAsync ->
ValidateDomains -> FindDomain) compares ConfiguredEndpoint.EndpointUrl.IdnHost
— the CONFIGURED host, because OpcUaEndpointSelection/EndpointSelector
rewrote the advertised one — against the cert's DNS/IP SANs; secured
sessions only, and the auto-accept handler accepts a mismatch.
Policy: certificateValidation.validateServerHostName, tri-state. Unset =
OpcUaCertificateValidationOptions.DefaultValidateServerHostName = false, the
pre-#816 behaviour, so nothing changes on upgrade; true = validate the
configured host; false = explicit NAT/port-publish opt-out. Threaded into the
driver, the AdminUI browser (same JSON) and the AdminUI form (a select that
keeps "unset" unset), Client.Shared ConnectionSettings.ValidateServerHostName
and the CLI --validate-host-name. A driver refusal names the opt-out.
#818: the NAT fixture's /app/pki is on the opc-plc-nat-pki volume (verified:
same thumbprint across --force-recreate), its PUBLIC cert is committed as
Docker/nat/opc-plc-nat-server.der, and NatPublishedEndpointBrowseTests run
every secure browse on a throwaway PKI (internal browser seam): refusal with
nothing trusted, positive with the cert trusted (unset/false host check), and
a BadCertificateHostNameInvalid refusal with the check on. The trusted cert is
OPCUA_NAT_SERVER_CERT or the committed one (skip on thumbprint mismatch);
OPCUA_NAT_SERVER_CERT_TRUSTED is retired. CI exports its throwaway NAT
container's public cert. ServerHostNameValidationTests pin the driver against
the plain opc-plc. MIN_EXECUTED not raised (needs a hosted run): +6 in
v2-integration (440 -> 446), documented in scripts/ci/README.md.
Joseph Doherty