feat(opcuaclient): opt-in server-certificate host-name check; NAT fixture keeps its PKI (#816, #818)

#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.
2026-11-11 01:33:00 -05:00
parent bde6cce2fc
commit ae91e6b7f7
30 changed files with 648 additions and 59 deletions
@@ -288,6 +288,13 @@ host logger factory (wired in `DriverFactoryBootstrap`; the FOCAS and TwinCAT fa
  AFTER configured ones; more than one discovered server without `discoveryServerUri` fails the connect. Session
  events are the OTel counter `otopcua.driver.opcuaclient.events`. `HistoryAggregateType` carries the full Part 13
  set; an aggregate the gateway can't serve is `BadAggregateNotSupported` per node.
 - **OpcUaClient server host-name check (#816):** the SDK checks the server certificate's host only with
  `checkDomain: true`; its 8-arg `DefaultSessionFactory.CreateAsync` hard-codes `false`, so driver, AdminUI browser and
  Client.Shared never checked before #816. Now `certificateValidation.validateServerHostName` (tri-state, unset = off =
  unchanged; AdminUI keeps it unset) / CLI `--validate-host-name`. It checks the **configured** host (the rewritten
  `ConfiguredEndpoint.EndpointUrl`), secured sessions only, and auto-accept accepts a mismatch. Any new session-create
  call site must pass the flag — the overload without it silently disables the check. The rewriter keeps an IPv6
  zone index verbatim (#819; .NET `Uri` drops it from every re-serialisation). `docs/drivers/OpcUaClient.md`.
 - **MTConnect (#627/#628):** TIME_SERIES reads as a variable-length `double[]` (Float64 only); a count disagreeing
  with `sampleCount` is `BadDecodingError`. One MTConnect driver = one agent client = at most one `/raw` Device
  (`MTConnectMultipleDevices` deploy error; `RawTreeService.CreateDeviceAsync` refuses a second).
@@ -74,6 +74,8 @@ jobs:
      - name: assert not-all-skipped
        if: always()
        env:
          # #816/#818 added 6 executing OpcUaClient tests; raise to 446 once a hosted run confirms them
          # (scripts/ci/README.md §"Fixture-backed integration").
          MIN_EXECUTED: "440"
        run: bash scripts/ci/assert-not-all-skipped.sh artifacts/trx/*.trx
      - name: fixture logs on failure
@@ -39,6 +39,7 @@ All commands accept these options:
 | `-P` / `--password` | Password for `UserName` token authentication |
 | `-S` / `--security` | Transport security mode: `none`, `sign`, `encrypt`, `signandencrypt` (default: `none`) |
 | `-F` / `--failover-urls` | Comma-separated failover endpoint URLs for redundancy |
 | `--validate-host-name` | Require the server certificate to list the `--url` host (#816). Secured connections only; off by default (the CLI's long-standing behaviour). The CLI auto-accepts untrusted certificates, so this checks a misconfiguration, not trust. Leave off behind NAT / when connecting by an IP the certificate omits |
 | `--verbose` | Enable debug-level Serilog console logging (default: warning) |
 **`--security none` does not fall back.** Endpoint selection picks the server's `None`-policy endpoint and
@@ -108,7 +108,14 @@ The rule, for `opc.tcp` (and any scheme, as long as advertised and configured sc
  a real rewrite keeps the advertised path's percent-escaping (`AbsoluteUri`, #812);
 - a **different scheme** (an `https` endpoint next to an `opc.tcp` one) is a different transport and is left alone;
 - an unusable advertised URL (null / blank / unparseable) falls back to the configured one in the driver and the
-  browser; the Client CLI/UI instead reports it (it validates before calling the rewriter).
+  browser; the Client CLI/UI instead reports it (it validates before calling the rewriter);
 - an **IPv6 zone index** on the configured host (`opc.tcp://[fe80::1%eth0]:4840`) is **kept, verbatim** (#819).
  .NET's `Uri` parses the zone but drops it from `Host`/`Authority`/`AbsoluteUri`/`ToString()` — only
  `DnsSafeHost`/`IdnHost` carry it — so the rewriter splices it back into the string. The SDK dials
  `new Uri(EndpointUrl).IdnHost` (`TcpByteTransport` → `DnsEndPoint`), which keeps it, so a link-local endpoint now
  routes; before #819 the session dialled a zone-less `fe80::` address. The zone text is not normalised: write the
  form your OS resolves (`%eth0` / `%4`). .NET does **not** decode RFC 6874's `%25eth0` (its `DnsSafeHost` is
  `fe80::1%25eth0`), so that form is passed through as written — GetEndpoints and the session see the same string.
 **What the rewrite does NOT touch.** It only chooses the network address. The **security policy and mode** are
 still selected from the server's advertisement exactly as before — the driver and browser filter on the configured
@@ -118,7 +125,51 @@ user-token policies** are the advertised ones. **Certificate validation is uncha
 validates the certificate of the server actually reached, against the same trust store (the driver's PKI, the
 browse picker's separate `adminui-browse-pki`, the CLI's own) with the same `AutoAcceptCertificates` semantics. The
 NAT tests below pin that a secure browse through the NAT is refused on an untrusted certificate and succeeds once it
-is trusted.
+is trusted. The optional **host-name** check (#816, next section) is the one place the rewrite matters to validation:
 it runs against the rewritten URL, i.e. the **configured** host.
 ### Server certificate host name (#816)
 **Finding (SDK 2.0.1).** The SDK only checks that the server certificate names the host you connected to when the
 session is created with `checkDomain: true`. All three surfaces — the driver (`OpenSessionOnEndpointAsync`), the
 AdminUI browser (`OpcUaClientDriverBrowser.OpenAsync`) and Client.Shared (`DefaultSessionFactory`) — called the
 8-argument `DefaultSessionFactory.CreateAsync(config, endpoint, updateBeforeConnect, sessionName, …)`, which
 forwards `checkDomain: false`. So **no host-name check ever ran**; trust was the trusted-peer / issuer store alone.
 That is why, in #813, a trusted NAT certificate for `otopcua-opc-plc-nat-private.invalid` browsed fine over an IP.
 Where the check lives when enabled: `Session.OpenAsync` → after `CertificateManager.ValidateAsync` accepts the chain,
 `if (checkDomain) CertificateValidationExtensions.ValidateDomains(validator, serverCert, session.ConfiguredEndpoint)`
 → `CertificateValidationCore.ValidateDomains` → `CertificateValidationHelpers.FindDomain`, which compares
 `ConfiguredEndpoint.EndpointUrl.IdnHost` with the certificate's DNS / IP SANs (IP literals normalised; a `localhost`
 / `127.0.0.1` / `::1` URL is compared as the machine's own host name + FQDN). A miss is `BadCertificateHostNameInvalid`
 ("The domain '…' is not listed in the server certificate."), passed to the certificate manager's `AcceptError` hook
 first. Consequences:
 - **It checks the CONFIGURED host.** `ConfiguredEndpoint.EndpointUrl` is the URL `OpcUaEndpointSelection` /
  `EndpointSelector` rewrote, so the advertised host the server named itself never takes part.
 - **Secured sessions only** — the block runs only when the channel (or the user-token policy) needs the server
  certificate; a `None` session validates no certificate at all.
 - **`autoAcceptCertificates` accepts a mismatch too** (the driver's auto-accept `AcceptError` handler returns `true`
  for everything but revocation). The Client CLI always auto-accepts.
 - Test Connect (`OpcUaClientDriverProbe`) only calls GetEndpoints on an unsecured discovery channel — no session, so no
  certificate or host-name check.
 **Policy: `certificateValidation.validateServerHostName`** (driver JSON; AdminUI driver form "Server host-name check";
 the browser reads the same JSON):
 | Value | Meaning |
 |---|---|
 | absent / `null` (**default**) | `OpcUaCertificateValidationOptions.DefaultValidateServerHostName` = **off** — exactly the pre-#816 behaviour, so no existing deployment changes on upgrade. The AdminUI form keeps it absent ("Default (off)") rather than writing a concrete `false`. |
 | `true` | Validate: the certificate must list the configured endpoint host. The driver's connect failure then appends the remedy (fix the certificate, connect by a name it lists, or opt out). |
 | `false` | Explicit opt-out — the NAT / container port-publish / connect-by-an-IP-the-cert-omits case. |
 When to turn it on: it earns its keep when trust comes from a **CA** (a trusted issuer vouches for every certificate
 it signed, so only the host check ties the certificate to *this* server). With the server's own self-signed
 certificate pinned in the trusted-peer store it adds little — the pin already identifies the server. Client
 CLI: `--validate-host-name` (`ConnectionSettings.ValidateServerHostName`, default `false`). Pinned by
 `ServerHostNameValidationTests` (driver vs. the plain opc-plc, whose certificate names only its container id) and
 `NatPublishedEndpointBrowseTests` (browser vs. the NAT opc-plc): unset/`false` connect, `true` is refused naming the
 configured host.
 **Running the NAT tests.** `NatPublishedEndpointBrowseTests`
 (`tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests`, `Fixture=opc-plc-nat`) run against
@@ -133,13 +184,20 @@ OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010 dotnet test \
    tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests --filter Fixture=opc-plc-nat
 ```
-The secure case asserts a certificate **refusal** by default. To make it positive, trust the fixture's server
+Every secure browse there runs on a **throwaway browse PKI** (an internal PKI-root seam on the browser), never your
-certificate in the browse PKI and set `OPCUA_NAT_SERVER_CERT_TRUSTED=1` — the certificate is regenerated whenever
+`adminui-browse-pki`. The refusal case trusts nothing and always runs. The positive case (unset / `false` host check)
-the container is recreated, so fetch the current one:
+and the host-name refusal (`true`) trust the fixture's **public** certificate (#818), from:
-`ssh dohertj2@10.100.0.35 'docker exec otopcua-opc-plc-nat sh -c "cat /app/pki/own/certs/*.der"' > "<LocalAppData>/OtOpcUa/adminui-browse-pki/trusted/certs/opc-plc-nat.der"`
+
-(`~/Library/Application Support/...` on macOS, `~/.local/share/...` on Linux), and delete it again afterwards. CI
+1. `OPCUA_NAT_SERVER_CERT` — a DER or PEM file; must be the certificate the server presents, or the test **fails**; else
-(`v2-integration.yml`) starts its own throwaway NAT copy (`scripts/ci/integration-fixtures.sh`); `v2-e2e.yml` points at
+2. the committed `tests/.../Driver.OpcUaClient.IntegrationTests/Docker/nat/opc-plc-nat-server.der` — the shared-host
-the shared one. Neither trusts the certificate, so CI runs the refusal form.
+   stack's certificate, stable because its PKI lives on the `opc-plc-nat-pki` volume. If it is not the certificate
   the server presents (another NAT fixture, or the stack's certificate was rolled) these tests **skip**.
 The private key never leaves the volume. The committed certificate expires **2027-11-10**; to roll it, see the comment
 at the top of `Docker/nat/docker-compose.yml`. CI (`v2-integration.yml`) starts its own throwaway NAT copy
 (`scripts/ci/integration-fixtures.sh`), copies that container's public certificate out with `docker exec` and exports
 `OPCUA_NAT_SERVER_CERT`, so it runs the positive cases too; `v2-e2e.yml` points at the shared stack and uses the
 committed certificate.
 ### Session lifetime
@@ -379,6 +437,7 @@ also refuses them explicitly — defence in depth (#277), not a behaviour change
 |---|---|---|
 | `rejectUnknownRevocationStatus` | `false` | Reject a server certificate whose revocation status cannot be determined (no CRL for its issuer, or a stale one). Leave `false` for brownfield sites without CRL infrastructure. **Only effective with `autoAcceptCertificates` off** — the auto-accept handler accepts every suppressible error, including revocation-unknown. |
 | `issuerStorePath` | `null` (= `%LocalAppData%/OtOpcUa/pki/issuers`) | Directory used as the trusted-issuer store. The SDK reads issuer CRLs (`*.crl`) from its `crl/` sub-folder, so this is how an operator points the driver at a managed CRL set. |
 | `validateServerHostName` | `null` (= off) | #816: require the server certificate to name the **configured** endpoint host (`BadCertificateHostNameInvalid` otherwise). Secured sessions only; accepted anyway under `autoAcceptCertificates`. `false` = explicit NAT opt-out. See "Server certificate host name" above. |
 ### Subscription tuning (#273)
@@ -280,8 +280,9 @@ Razor picker body          BrowserSessionService          IDriverBrowser
  (`ssh dohertj2@10.100.0.35 'cd /opt/otopcua-opcuaclient-nat && docker compose up -d'`, compose in
  `tests/.../Driver.OpcUaClient.IntegrationTests/Docker/nat/`), and CI starts a throwaway copy. Run:
  `OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010 dotnet test tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests --filter Fixture=opc-plc-nat`.
-  The secure case asserts a certificate refusal unless the fixture cert is trusted in the browse PKI and
+  The secure cases run on a throwaway browse PKI: a refusal with nothing trusted, and (#818) positive / #816
-  `OPCUA_NAT_SERVER_CERT_TRUSTED=1` (see `docs/drivers/OpcUaClient.md`).
+  host-name cases that trust the fixture's public certificate (`OPCUA_NAT_SERVER_CERT`, or the committed
  `Docker/nat/opc-plc-nat-server.der`) — see `docs/drivers/OpcUaClient.md`. (`OPCUA_NAT_SERVER_CERT_TRUSTED` is retired.)
 - No Galaxy integration suite in v1 (requires wonder-app-vd03; deferred)
 ### Specific regression tests
@@ -100,9 +100,12 @@ when it isn't running. Bring one up, `dotnet test`, tear down. Repo compose live
 > `NatPublishedEndpointBrowseTests` (Browser.IntegrationTests, `Fixture=opc-plc-nat`) use it, and each asserts that
 > premise before testing the shared `OpcUaEndpointUrlRewriter` (configured host:port win, advertised path kept):
 > `OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010 dotnet test tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests --filter Fixture=opc-plc-nat`.
-> A separate stack so it never touches `otopcua-opc-plc`; it carries the `project: lmxopcua` label. The secure case
+> A separate stack so it never touches `otopcua-opc-plc`; it carries the `project: lmxopcua` label. Its PKI is on the
-> turns positive with `OPCUA_NAT_SERVER_CERT_TRUSTED=1` once the container's cert is in the browse PKI
+> `opc-plc-nat-pki` volume (#818), so its certificate survives a recreate; the PUBLIC half is committed as
-> (`docs/drivers/OpcUaClient.md` §"Endpoint address"). CI runs its own throwaway copy (`otopcua-ci-opcplc-nat`, §10).
+> `Docker/nat/opc-plc-nat-server.der` and the positive secure / #816 host-name cases trust it in a throwaway browse PKI
 > (they skip if the server presents a different one; `OPCUA_NAT_SERVER_CERT=<file>` overrides). `docker compose down -v`
 > rolls the certificate — refresh the committed copy then (`docs/drivers/OpcUaClient.md` §"Endpoint address"). CI runs
 > its own throwaway copy (`otopcua-ci-opcplc-nat`, §10) and exports its certificate as `OPCUA_NAT_SERVER_CERT`.
 > **MTConnect is a TWO-service stack.** The `mtconnect/agent` image ships no simulator, so a lone
 > Agent answers `/probe` and reports every observation `UNAVAILABLE` forever. The `adapter` service
@@ -75,9 +75,19 @@ Neither touches `v2-ci.yml`; each has its own concurrency group (`lmxopcua-v2-in
  Local run: 468 executed / 8 skipped (Oracle x2, the blackhole `docker pause` gate, one QuestDB stress test,
  4 others), about 4.5 min of test time, QuestDB the longest (~3.3 min). Not covered (no pullable image or
  needs credentials): Modbus/S7/AB/FOCAS/TwinCAT sims, Mqtt, MTConnect, Oracle, Host real-infra mode.
  **#816/#818 added 6 executing tests here, floor NOT yet raised:** `ServerHostNameValidationTests` (3, vs the plain
  `otopcua-ci-opcplc`) and the NAT positive-secure / host-name cases (3, which run because `integration-fixtures.sh`
  now exports the NAT container's public certificate as `OPCUA_NAT_SERVER_CERT`). Locally (2026-11-11, shared host)
  the two OpcUaClient projects went 13 → 19 executed with 0 skipped, and `assert-not-all-skipped.sh` counted them.
  Once a hosted run's TRX shows `Driver.OpcUaClient.trx` executed=8 and `Driver.OpcUaClient.Browser.trx` executed=11,
  raise `MIN_EXECUTED` in `v2-integration.yml` **440 → 446**. If the NAT three show as skipped there, the certificate
  hand-off (`docker exec … /app/pki/own/certs/*.der`) did not work on the runner — fix that, do not lower the bump.
 - **`v2-e2e.yml`** (manual + weekly cron only; `timeout-minutes: 90`). `probe-e2e-fixtures.sh` TCP-probes
  10.100.0.35 ports 5020/1102/50000; if any is closed every later step is skipped and the run is green with a
  notice. Otherwise runs the Modbus, S7, OpcUaClient and OpcUaClient.Browser integration projects against the
-  shared fleet with `MIN_EXECUTED=35` (`OPCUA_NAT_ENDPOINT` points at the shared NAT stack on :50010; its 3 tests
+  shared fleet with `MIN_EXECUTED=35` (`OPCUA_NAT_ENDPOINT` points at the shared NAT stack on :50010; its 6 tests
-  skip if it is down, so it is not a probe-required port) (local: 42 executed / 38 skipped; Modbus skips the profiles that are not
+  skip if it is down, so it is not a probe-required port — and its 3 certificate-trusting ones also skip if the stack's
  certificate no longer matches the committed `Docker/nat/opc-plc-nat-server.der`, so do not count them in the floor;
  #816's 3 `ServerHostNameValidationTests` need only the probe-required :50000, so this floor may go **35 → 38** after
  a hosted run shows them executed) (local: 42 executed / 38 skipped; Modbus skips the profiles that are not
  up). No test carries `Category=E2E` today, so the zero-match guard is this executed floor.
@@ -80,6 +80,14 @@ up() {
  wait_for "questdb" 120 curl -fsS "http://$(fixture_host):$QDB_HTTP_PORT/exec?query=select%201"
  wait_for "opc-plc" 120 bash -c "exec 3<>/dev/tcp/$(fixture_host)/$OPC_PORT"
  wait_for "opc-plc (NAT)" 120 bash -c "exec 3<>/dev/tcp/$(fixture_host)/$OPC_NAT_PORT"
  # #818: hand the NAT server's PUBLIC certificate to NatPublishedEndpointBrowseTests (OPCUA_NAT_SERVER_CERT) so the
  # positive secure / host-name cases run here too. Copied out of the container — the trust channel is docker itself,
  # not the wire. The throwaway container makes a fresh certificate per run, so the committed shared-host copy cannot
  # be used; the private key never leaves the container.
  local nat_cert="${RUNNER_TEMP:-${TMPDIR:-/tmp}}/otopcua-ci-fixtures/opc-plc-nat-server.der"
  mkdir -p "$(dirname "$nat_cert")"
  wait_for "opc-plc (NAT) certificate" 60 bash -c \
    "docker exec otopcua-ci-opcplc-nat bash -c 'cat /app/pki/own/certs/*.der' > '$nat_cert' && [ -s '$nat_cert' ]"
  local h; h="$(fixture_host)"
  local -a exports=(
@@ -92,6 +100,7 @@ up() {
    "HISTORIAN_QUESTDB_TEST_CONNECTION=Host=$h;Port=$QDB_PORT;Username=admin;Password=quest;Database=qdb;ServerCompatibilityMode=NoTypeLoading"
    "OPCUA_SIM_ENDPOINT=opc.tcp://$h:$OPC_PORT"
    "OPCUA_NAT_ENDPOINT=opc.tcp://$h:$OPC_NAT_PORT"
    "OPCUA_NAT_SERVER_CERT=$nat_cert"
  )
  for e in "${exports[@]}"; do
    echo "export \"$e\""
@@ -57,6 +57,13 @@ public abstract class CommandBase : ICommand
    [CommandOption("failover-urls", 'F', Description = "Comma-separated failover endpoint URLs for redundancy")]
    public string? FailoverUrls { get; init; }
    /// <summary>
    /// Gets a value indicating whether the server certificate must name the host given in <see cref="Url" /> (#816).
    /// </summary>
    [CommandOption("validate-host-name",
        Description = "Require the server certificate to list the --url host (secured connections only; off by default — leave off behind NAT)")]
    public bool ValidateHostName { get; init; }
    /// <summary>
    /// Gets a value indicating whether verbose Serilog output should be enabled for troubleshooting.
    /// </summary>
@@ -88,7 +95,8 @@ public abstract class CommandBase : ICommand
            Username = Username,
            Password = Password,
            SecurityMode = securityMode,
-            AutoAcceptCertificates = true
+            AutoAcceptCertificates = true,
            ValidateServerHostName = ValidateHostName
        };
        return settings;
@@ -18,6 +18,7 @@ internal sealed class DefaultSessionFactory : ISessionFactory
        string sessionName,
        uint sessionTimeoutMs,
        UserIdentity identity,
        bool validateServerHostName,
        CancellationToken ct)
    {
        var endpointConfig = EndpointConfiguration.Create(config);
@@ -26,7 +27,10 @@ internal sealed class DefaultSessionFactory : ISessionFactory
        var created = await new Opc.Ua.Client.DefaultSessionFactory(ClientTelemetry.Context).CreateAsync(
            config,
            configuredEndpoint,
-            false,
+            false,                       // updateBeforeConnect
            // #816: the overload without checkDomain hard-codes false. The endpoint URL here is the operator's host
            // (EndpointSelector rewrote the advertised one), so that is the host the certificate is checked against.
            validateServerHostName,      // checkDomain
            sessionName,
            sessionTimeoutMs,
            identity,
@@ -15,6 +15,9 @@ internal interface ISessionFactory
    /// <param name="sessionName">The session name.</param>
    /// <param name="sessionTimeoutMs">Session timeout in milliseconds.</param>
    /// <param name="identity">The user identity.</param>
    /// <param name="validateServerHostName">
    ///     The SDK's <c>checkDomain</c>: require the server certificate to name the endpoint URL's host (#816).
    /// </param>
    /// <param name="ct">Cancellation token.</param>
    /// <returns>A session adapter wrapping the created session.</returns>
    Task<ISessionAdapter> CreateSessionAsync(
@@ -23,5 +26,6 @@ internal interface ISessionFactory
        string sessionName,
        uint sessionTimeoutMs,
        UserIdentity identity,
        bool validateServerHostName,
        CancellationToken ct = default);
 }
@@ -40,6 +40,15 @@ public sealed class ConnectionSettings
    /// </summary>
    public bool AutoAcceptCertificates { get; set; } = true;
    /// <summary>
    ///     Gitea #816 — require the server certificate to list the host of the URL being connected (the operator's
    ///     host: discovery keeps it in place of the server-advertised one) among its subject-alternative names;
    ///     a mismatch fails the connect with <c>BadCertificateHostNameInvalid</c>. Defaults to <c>false</c>, the
    ///     behaviour before #816 (the SDK overload used never checked). Secured connections only. Leave it off behind
    ///     NAT / a port publish / when connecting by an IP the certificate does not name.
    /// </summary>
    public bool ValidateServerHostName { get; set; }
    /// <summary>
    ///     Path to the certificate store. Defaults to <see cref="string.Empty"/>; the
    ///     consuming application configuration factory resolves the canonical path via
@@ -777,6 +777,7 @@ public sealed class OpcUaClientService : IOpcUaClientService
            SecurityMode = settings.SecurityMode,
            SessionTimeoutSeconds = settings.SessionTimeoutSeconds,
            AutoAcceptCertificates = settings.AutoAcceptCertificates,
            ValidateServerHostName = settings.ValidateServerHostName,
            CertificateStorePath = settings.CertificateStorePath,
            Username = settings.Username,
            Password = settings.Password
@@ -794,7 +795,7 @@ public sealed class OpcUaClientService : IOpcUaClientService
            var sessionTimeoutMs = (uint)(settings.SessionTimeoutSeconds * 1000);
            return await _sessionFactory.CreateSessionAsync(config, endpoint, "OtOpcUaClient", sessionTimeoutMs, identity,
-                ct);
+                settings.ValidateServerHostName, ct);
        }
        catch
        {
@@ -35,6 +35,7 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
    private readonly ILogger<OpcUaClientDriverBrowser> _logger;
    private readonly ISecretResolver? _secretResolver;
    private readonly string? _pkiRootOverride;
    /// <summary>Creates a new browser. Logger defaults to NullLogger when not supplied.</summary>
    /// <param name="logger">Optional logger; defaults to <see cref="NullLogger{T}"/>.</param>
@@ -49,6 +50,18 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
        _secretResolver = secretResolver;
    }
    /// <summary>
    ///     Test seam (Gitea #818): a browser whose PKI lives under <paramref name="pkiRoot"/> instead of the shared
    ///     <c>%LocalAppData%/OtOpcUa/adminui-browse-pki</c>, so an integration test can trust a fixture's public
    ///     certificate in a throwaway store without touching the operator's browse trust list.
    /// </summary>
    /// <param name="pkiRoot">Directory holding the <c>own</c>/<c>trusted</c>/<c>issuers</c>/<c>rejected</c> stores.</param>
    internal OpcUaClientDriverBrowser(string pkiRoot) : this()
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(pkiRoot);
        _pkiRootOverride = pkiRoot;
    }
    /// <inheritdoc />
    //     Sourced from the shared DriverTypeNames set rather than the hand-written literal
    //     this line used to carry. The value is unchanged; the constant is what
@@ -82,7 +95,7 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
                    "driver's PKI store instead.",
                    endpoint);
-            var app = await BuildBrowseAppConfigurationAsync(cancellationToken).ConfigureAwait(false);
+            var app = await BuildBrowseAppConfigurationAsync(_pkiRootOverride, cancellationToken).ConfigureAwait(false);
            ownedApplication = app;
            var appConfig = app.ApplicationConfiguration!;
@@ -101,6 +114,9 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
                appConfig,
                configuredEndpoint,
                updateBeforeConnect: false,
                // Gitea #816: the same host-name policy as the deployed driver (the SDK's overload without this
                // argument hard-codes false), checked against the configured host the endpoint was rewritten to.
                checkDomain: opts.CertificateValidation.EffectiveValidateServerHostName,
                sessionName: "OtOpcUa AdminUI Browse",
                (uint)opts.SessionTimeout.TotalMilliseconds,
                identity,
@@ -143,8 +159,10 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
    ///     the runtime driver (<c>%LocalAppData%/OtOpcUa/adminui-browse-pki/</c>). Browse
    ///     trust decisions don't leak into the deployed driver's cert store.
    /// </summary>
    /// <param name="pkiRootOverride">Test-only PKI root; <c>null</c> = the shared browse PKI.</param>
    /// <param name="ct">Cancellation token for the configuration build.</param>
-    private static async Task<ApplicationInstance> BuildBrowseAppConfigurationAsync(CancellationToken ct)
+    private static async Task<ApplicationInstance> BuildBrowseAppConfigurationAsync(
        string? pkiRootOverride, CancellationToken ct)
    {
        // The ITelemetryContext overload is the non-obsolete ctor; an empty builder keeps SDK
        // internals off any logging provider.
@@ -154,7 +172,7 @@ public sealed class OpcUaClientDriverBrowser : IDriverBrowser
            ApplicationType = ApplicationType.Client,
        };
-        var pkiRoot = Path.Combine(
+        var pkiRoot = pkiRootOverride ?? Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
            "OtOpcUa", "adminui-browse-pki");
@@ -19,5 +19,6 @@
    </ItemGroup>
    <ItemGroup>
        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests"/>
        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests"/>
    </ItemGroup>
 </Project>
@@ -231,6 +231,35 @@ public sealed record OpcUaCertificateValidationOptions
    ///     operator-managed CRL set. <c>null</c>/empty (default) = <c>%LocalAppData%/OtOpcUa/pki/issuers</c>.
    /// </summary>
    public string? IssuerStorePath { get; init; }
    /// <summary>
    ///     The value an unset <see cref="ValidateServerHostName"/> resolves to. <c>false</c> keeps the behaviour every
    ///     deployment had before Gitea #816 (the SDK never checked the host name for this driver family).
    /// </summary>
    public const bool DefaultValidateServerHostName = false;
    /// <summary>
    ///     Gitea #816 — whether the server certificate must list the host the operator CONFIGURED (the endpoint URL's
    ///     host, which the shared <see cref="OpcUaEndpointUrlRewriter"/> keeps in place of the server-advertised one)
    ///     among its DNS / IP subject-alternative names. A mismatch refuses the session with
    ///     <c>BadCertificateHostNameInvalid</c>.
    ///     <list type="bullet">
    ///         <item><c>null</c> (default) = <see cref="DefaultValidateServerHostName"/> (off).</item>
    ///         <item><c>true</c> = validate. Worth it when trust comes from a CA (a trusted issuer vouches for every
    ///         certificate it signed, so only the host check ties the certificate to THIS server); adds little when the
    ///         server's own self-signed certificate is pinned in the trusted-peer store.</item>
    ///         <item><c>false</c> = explicit opt-out — the NAT / port-publish / IP-addressed case, where the server's
    ///         certificate names its private host and the reachable address is something else.</item>
    ///     </list>
    ///     Only applies to secured sessions (a <c>None</c> channel validates no server certificate at all), and
    ///     <see cref="OpcUaClientDriverOptions.AutoAcceptCertificates"/> accepts a host-name mismatch like any other
    ///     certificate error.
    /// </summary>
    public bool? ValidateServerHostName { get; init; }
    /// <summary><see cref="ValidateServerHostName"/> with the default applied.</summary>
    [System.Text.Json.Serialization.JsonIgnore]
    public bool EffectiveValidateServerHostName => ValidateServerHostName ?? DefaultValidateServerHostName;
 }
 /// <summary>OPC UA message security mode.</summary>
@@ -581,7 +581,7 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
                catch (OperationCanceledException) when (cancellationToken.IsCancellationRequested) { throw; }
                catch (Exception ex)
                {
-                    attemptErrors.Add($"{url} -> {ex.GetType().Name}: {ex.Message}");
+                    attemptErrors.Add($"{url} -> {ex.GetType().Name}: {ex.Message}{HostNameRefusalHint(ex)}");
                }
            }
@@ -726,6 +726,14 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
    private void WriteLifecycleHealth(long generation, Func<DriverHealth, DriverHealth> next) =>
        UpdateHealth(generation, next);
    /// <summary>
    ///     Test seam (Gitea #816): when set, the PKI stores live under this directory instead of the shared
    ///     <c>%LocalAppData%/OtOpcUa/pki</c>, so an integration test can trust a fixture's certificate in a throwaway
    ///     store with <see cref="OpcUaClientDriverOptions.AutoAcceptCertificates"/> off (auto-accept also accepts a
    ///     host-name mismatch, which would hide the check under test). Set before <c>InitializeAsync</c>.
    /// </summary>
    internal string? PkiRootOverride { get; set; }
    /// <summary>
    ///     Build a minimal in-memory <see cref="ApplicationConfiguration"/>. Certificates live
    ///     under the OS user profile — on Windows that's <c>%LocalAppData%\OtOpcUa\pki</c>
@@ -747,7 +755,7 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
        };
        certValidation.Application = app;
-        var pkiRoot = Path.Combine(
+        var pkiRoot = PkiRootOverride ?? Path.Combine(
            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
            "OtOpcUa", "pki");
@@ -1051,10 +1059,14 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
        endpointConfig.OperationTimeout = (int)_options.Timeout.TotalMilliseconds;
        var endpoint = new ConfiguredEndpoint(null, selected, endpointConfig);
        // Gitea #816: the SDK's 8-argument CreateAsync hard-codes checkDomain:false, so before #816 the server
        // certificate's host name was never checked. The check (when enabled) runs against endpoint.EndpointUrl —
        // the CONFIGURED host, because SelectMatching rewrote the advertised one.
        var session = await new DefaultSessionFactory(_sdkTelemetry).CreateAsync(
            appConfig,
            endpoint,
            false,                                              // updateBeforeConnect
            _options.CertificateValidation.EffectiveValidateServerHostName, // checkDomain (#816)
            _options.SessionName,
            (uint)_options.SessionTimeout.TotalMilliseconds,
            identity,
@@ -1085,6 +1097,19 @@ public sealed class OpcUaClientDriver : IDriver, ITagDiscovery, IReadable, IWrit
        return OpcUaEndpointSelection.SelectMatching(all.ToList(), endpointUrl, policy, mode);
    }
    /// <summary>
    ///     Gitea #816 — the operator-facing remedy appended to a <c>BadCertificateHostNameInvalid</c> connect failure (only
    ///     reachable with <c>certificateValidation.validateServerHostName</c> on). The SDK's own text names the host it
    ///     checked but not the knob.
    /// </summary>
    /// <param name="ex">The per-endpoint connect failure.</param>
    /// <returns>The hint, or an empty string for any other failure.</returns>
    internal static string HostNameRefusalHint(Exception ex) =>
        ex is ServiceResultException sre && sre.StatusCode == StatusCodes.BadCertificateHostNameInvalid
            ? " (the server certificate does not name the configured endpoint host; add that host to the certificate, " +
              "connect by a name it lists, or — behind NAT / a port publish — set certificateValidation.validateServerHostName=false)"
            : string.Empty;
    /// <summary>Delegates to the shared <see cref="OpcUaEndpointUrlRewriter.Rewrite"/> (Gitea #676 / #806).</summary>
    /// <param name="advertisedUrl">The <c>EndpointUrl</c> the server returned from GetEndpoints.</param>
    /// <param name="configuredUrl">The URL the driver was configured with (the one GetEndpoints was sent to).</param>
@@ -28,6 +28,8 @@
    <ItemGroup>
        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests"/>
        <!-- Gitea #816: the host-name tests trust the fixture certificate in a throwaway PKI (PkiRootOverride). -->
        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests"/>
        <!-- Gitea #656: the native-alarm re-statement end-to-end tests drive this driver into the real DriverHostActor. -->
        <InternalsVisibleTo Include="ZB.MOM.WW.OtOpcUa.Runtime.Tests"/>
        <!-- Gitea #670 review M1: the wire test deletes the driver's subscription server-side through its own session. -->
@@ -192,6 +192,15 @@
                </div>
                <div class="form-text">Revoked certificates are always rejected.</div>
            </div>
            <div class="col-md-3">
                <label class="form-label">Server host-name check</label>
                <InputSelect @bind-Value="_form.OpcUa.ValidateServerHostName" @bind-Value:after="EmitAsync" class="form-select form-select-sm">
                    <option value="">Default (off)</option>
                    <option value="true">Validate configured host</option>
                    <option value="false">Off (NAT / port publish)</option>
                </InputSelect>
                <div class="form-text">Secured sessions only: the server certificate must name the endpoint host you configured.</div>
            </div>
            <div class="col-md-6">
                <label class="form-label">Issuer store / CRL directory</label>
                <InputText @bind-Value="_form.OpcUa.IssuerStorePath" @bind-Value:after="EmitAsync" class="form-control form-control-sm mono" />
@@ -349,6 +358,8 @@
        public int SubscriptionPriority { get; set; }
        public bool RejectUnknownRevocationStatus { get; set; }
        public string? IssuerStorePath { get; set; }
        // #816 tri-state: "" = unset (the driver default) so the form never re-emits a concrete default; "true"/"false".
        public string ValidateServerHostName { get; set; } = "";
        public string? DiscoveryUrl { get; set; }
        public string? DiscoveryServerUri { get; set; }
@@ -381,6 +392,12 @@
            SubscriptionPriority = r.SubscriptionPriority,
            RejectUnknownRevocationStatus = r.CertificateValidation.RejectUnknownRevocationStatus,
            IssuerStorePath = r.CertificateValidation.IssuerStorePath,
            ValidateServerHostName = r.CertificateValidation.ValidateServerHostName switch
            {
                true => "true",
                false => "false",
                null => "",
            },
            DiscoveryUrl = r.DiscoveryUrl,
            DiscoveryServerUri = r.DiscoveryServerUri,
        };
@@ -417,6 +434,12 @@
            {
                RejectUnknownRevocationStatus = RejectUnknownRevocationStatus,
                IssuerStorePath = string.IsNullOrWhiteSpace(IssuerStorePath) ? null : IssuerStorePath,
                ValidateServerHostName = ValidateServerHostName switch
                {
                    "true" => true,
                    "false" => false,
                    _ => null,
                },
            },
            DiscoveryUrl = string.IsNullOrWhiteSpace(DiscoveryUrl) ? null : DiscoveryUrl,
            DiscoveryServerUri = string.IsNullOrWhiteSpace(DiscoveryServerUri) ? null : DiscoveryServerUri,
@@ -38,6 +38,22 @@ public class CommandBaseTests
        settings.AutoAcceptCertificates.ShouldBeTrue();
    }
    /// <summary>Gitea #816: --validate-host-name maps to the server host-name check, which is off without it.</summary>
    [Theory]
    [InlineData(false)]
    [InlineData(true)]
    public async Task ValidateHostNameOption_MapsToConnectionSettings(bool flag)
    {
        var fakeService = new FakeOpcUaClientService();
        var factory = new FakeOpcUaClientServiceFactory(fakeService);
        var command = new ConnectCommand(factory) { Url = "opc.tcp://localhost:4840", ValidateHostName = flag };
        using var console = TestConsoleHelper.CreateConsole();
        await command.ExecuteAsync(console);
        fakeService.LastConnectionSettings!.ValidateServerHostName.ShouldBe(flag);
    }
    /// <summary>Verifies that encrypt option maps to SignAndEncrypt.</summary>
    [Fact]
    public async Task SecurityOption_Encrypt_MapsToSignAndEncrypt()
@@ -14,6 +14,8 @@ internal sealed class FakeSessionFactory : ISessionFactory
    public bool ThrowOnCreate { get; set; }
    /// <summary>Gets the endpoint URL from the last CreateSessionAsync call.</summary>
    public string? LastEndpointUrl { get; private set; }
    /// <summary>Gets the host-name-validation flag from the last CreateSessionAsync call (#816).</summary>
    public bool? LastValidateServerHostName { get; private set; }
    /// <summary>
    /// Optional gate that, when set, blocks <see cref="CreateSessionAsync" /> until completed.
@@ -33,14 +35,16 @@ internal sealed class FakeSessionFactory : ISessionFactory
    /// <param name="sessionName">The session name.</param>
    /// <param name="sessionTimeoutMs">The session timeout in milliseconds.</param>
    /// <param name="identity">The user identity.</param>
    /// <param name="validateServerHostName">The SDK checkDomain flag (#816).</param>
    /// <param name="ct">Cancellation token.</param>
    /// <returns>A task containing the session adapter.</returns>
    public async Task<ISessionAdapter> CreateSessionAsync(
        ApplicationConfiguration config, EndpointDescription endpoint, string sessionName,
-        uint sessionTimeoutMs, UserIdentity identity, CancellationToken ct)
+        uint sessionTimeoutMs, UserIdentity identity, bool validateServerHostName, CancellationToken ct)
    {
        CreateCallCount++;
        LastEndpointUrl = endpoint.EndpointUrl ?? string.Empty;
        LastValidateServerHostName = validateServerHostName;
        // One-shot: the gate holds only the call that observed it, so a later call (e.g. a user's Connect while a
        // failover is held) runs freely.
@@ -55,6 +55,25 @@ public class OpcUaClientServiceTests : IDisposable
        _service.CurrentConnectionInfo.ShouldBe(info);
    }
    /// <summary>
    /// Gitea #816: the host-name check reaches the session factory (the SDK's checkDomain) — off by default, the
    /// pre-#816 behaviour — and survives the per-endpoint settings copy the connect path makes.
    /// </summary>
    [Theory]
    [InlineData(null)]
    [InlineData(true)]
    [InlineData(false)]
    public async Task ConnectAsync_threads_ValidateServerHostName_to_the_session(bool? validate)
    {
        var settings = ValidSettings();
        if (validate is { } v) settings.ValidateServerHostName = v;
        await _service.ConnectAsync(settings, TestContext.Current.CancellationToken);
        _sessionFactory.LastValidateServerHostName.ShouldBe(validate ?? false);
        _configFactory.LastSettings!.ValidateServerHostName.ShouldBe(validate ?? false);
    }
    /// <summary>
    /// Verifies that invalid connection settings fail validation before any OPC UA session is created.
    /// </summary>
@@ -1,5 +1,6 @@
 using System.Net;
 using System.Net.Sockets;
 using System.Security.Cryptography.X509Certificates;
 using Opc.Ua;
 using Opc.Ua.Client;
 using Shouldly;
@@ -20,27 +21,54 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests;
 ///     # or locally / in CI (scripts/ci/integration-fixtures.sh starts the same shape as otopcua-ci-opcplc-nat):
 ///     docker run -d --rm --name otopcua-806-nat --hostname otopcua-806-nat-parity -p 32781:50000 \
 ///         mcr.microsoft.com/iotedge/opc-plc:2.14.10 --pn=50000 --ph=otopcua-806-nat-parity.invalid --autoaccept --ut
-///     OPCUA_NAT_ENDPOINT=opc.tcp://127.0.0.1:32781 dotnet test --filter Fixture=opc-plc-nat
+///     docker exec otopcua-806-nat bash -c 'cat /app/pki/own/certs/*.der' &gt; /tmp/nat.der   # public cert only
 ///     OPCUA_NAT_ENDPOINT=opc.tcp://127.0.0.1:32781 OPCUA_NAT_SERVER_CERT=/tmp/nat.der dotnet test --filter Fixture=opc-plc-nat
 ///     </code>
 ///     Skipped unless <c>OPCUA_NAT_ENDPOINT</c> is set and accepts TCP. Every test first proves the premise (the
 ///     advertised URL is NOT the configured host:port, and its host does not resolve here), so a fixture that
 ///     advertises a reachable address cannot make these pass vacuously. Before the fix the positive cases failed with
 ///     <c>SocketException: nodename nor servname provided, or not known</c>.
 ///     <para><b>Secure cases (#813/#816/#818).</b> Every browse here runs on a THROWAWAY browse PKI (the browser's
 ///     internal PKI-root seam), never the operator's <c>adminui-browse-pki</c>. The refusal case trusts nothing. The
 ///     positive and host-name cases trust the fixture's PUBLIC certificate — from <c>OPCUA_NAT_SERVER_CERT</c> (a DER or
 ///     PEM file; what CI exports after copying it out of its throwaway container) or else the committed
 ///     <c>Docker/nat/opc-plc-nat-server.der</c> (the shared-host stack's certificate, stable since #818 put its PKI on a
 ///     volume) — and SKIP when the committed certificate is not the one the server presents, so they can never pass
 ///     against a different server.</para>
 /// </summary>
 [Trait("Category", "Integration"), Trait("Fixture", "opc-plc-nat")]
-public sealed class NatPublishedEndpointBrowseTests
+public sealed class NatPublishedEndpointBrowseTests : IDisposable
 {
    private const string EnvVar = "OPCUA_NAT_ENDPOINT";
    private const string CertEnvVar = "OPCUA_NAT_SERVER_CERT";
    private const string CommittedCertFile = "opc-plc-nat-server.der";
    private readonly string _pkiRoot = Path.Combine(Path.GetTempPath(), "otopcua-nat-pki-" + Guid.NewGuid().ToString("N"));
    private static string? Endpoint => Environment.GetEnvironmentVariable(EnvVar) is { Length: > 0 } e ? e : null;
-    private static string Json(string endpoint, string policy = "None", string mode = "None") => $$"""
+    /// <inheritdoc />
-        {
+    public void Dispose()
-            "EndpointUrl":"{{endpoint}}",
+    {
-            "SecurityPolicy":"{{policy}}","SecurityMode":"{{mode}}","AuthType":"Anonymous",
+        try { Directory.Delete(_pkiRoot, recursive: true); } catch { /* best-effort temp cleanup */ }
-            "SessionTimeout":"00:01:00","Timeout":"00:00:10","PerEndpointConnectTimeout":"00:00:10"
+    }
-        }
+
-        """;
+    /// <summary>A browser on this test's throwaway PKI.</summary>
    private OpcUaClientDriverBrowser Browser() => new(_pkiRoot);
    private static string Json(string endpoint, string policy = "None", string mode = "None", bool? validateHostName = null)
    {
        var certValidation = validateHostName is { } v
            ? $$""","CertificateValidation":{"ValidateServerHostName":{{(v ? "true" : "false")}}}"""
            : "";
        return $$"""
            {
                "EndpointUrl":"{{endpoint}}",
                "SecurityPolicy":"{{policy}}","SecurityMode":"{{mode}}","AuthType":"Anonymous",
                "SessionTimeout":"00:01:00","Timeout":"00:00:10","PerEndpointConnectTimeout":"00:00:10"{{certValidation}}
            }
            """;
    }
    private static string RequireFixture()
    {
@@ -60,8 +88,11 @@ public sealed class NatPublishedEndpointBrowseTests
        return endpoint;
    }
-    /// <summary>The premise: the server advertises a host:port other than the configured one, and that host is unresolvable.</summary>
+    /// <summary>
-    private static async Task AssertAdvertisesUnreachableAddressAsync(string endpoint, CancellationToken ct)
+    ///     The premise: the server advertises a host:port other than the configured one, and that host is unresolvable.
    ///     Returns the DER certificate the server presents on its secure endpoint.
    /// </summary>
    private static async Task<byte[]> AssertAdvertisesUnreachableAddressAsync(string endpoint, CancellationToken ct)
    {
        var appConfig = new ApplicationConfiguration(DefaultTelemetry.Create(_ => { }))
        {
@@ -84,6 +115,61 @@ public sealed class NatPublishedEndpointBrowseTests
            await Should.ThrowAsync<SocketException>(() => Dns.GetHostAddressesAsync(advertised.Host, ct),
                $"advertised host '{advertised.Host}' must be unresolvable from here, or this test proves nothing");
        }
        return endpoints.First(e => e.SecurityPolicyUri == SecurityPolicies.Basic256Sha256).ServerCertificate.ToArray();
    }
    /// <summary>
    ///     Trust the fixture's public certificate in this test's throwaway PKI, or SKIP when no certificate for THIS
    ///     server is available (see the class remarks). An explicit <c>OPCUA_NAT_SERVER_CERT</c> that does not match
    ///     FAILS: it names the certificate the operator meant, so a mismatch is a fixture problem worth seeing.
    /// </summary>
    /// <param name="presentedDer">The certificate the server presents (from its GetEndpoints answer).</param>
    private void TrustFixtureCertificate(byte[] presentedDer)
    {
        using var presented = X509CertificateLoader.LoadCertificate(presentedDer);
        X509Certificate2 trusted;
        if (Environment.GetEnvironmentVariable(CertEnvVar) is { Length: > 0 } path)
        {
            trusted = LoadPublicCertificate(path);
            trusted.Thumbprint.ShouldBe(presented.Thumbprint,
                $"{CertEnvVar}={path} is not the certificate the NAT fixture presents");
        }
        else
        {
            var committed = Path.Combine(AppContext.BaseDirectory, CommittedCertFile);
            if (!File.Exists(committed))
                Assert.Skip($"{CommittedCertFile} is not deployed next to the tests and {CertEnvVar} is unset.");
            trusted = LoadPublicCertificate(committed);
            if (trusted.Thumbprint != presented.Thumbprint)
                Assert.Skip($"the committed {CommittedCertFile} ({trusted.Thumbprint}) is not this fixture's certificate " +
                            $"({presented.Thumbprint}, expires {presented.NotAfter:yyyy-MM-dd}); set {CertEnvVar} or " +
                            "refresh the committed copy (see Docker/nat/docker-compose.yml).");
        }
        using (trusted)
        {
            trusted.HasPrivateKey.ShouldBeFalse("only a PUBLIC certificate is ever trusted from a file");
            var certs = Path.Combine(_pkiRoot, "trusted", "certs");
            Directory.CreateDirectory(certs);
            File.WriteAllBytes(Path.Combine(certs, "opc-plc-nat.der"), trusted.RawData);
        }
    }
    private static X509Certificate2 LoadPublicCertificate(string path)
    {
        var bytes = File.ReadAllBytes(path);
        var text = System.Text.Encoding.ASCII.GetString(bytes);
        return text.Contains("-----BEGIN CERTIFICATE-----", StringComparison.Ordinal)
            ? X509Certificate2.CreateFromPem(text)
            : X509CertificateLoader.LoadCertificate(bytes);
    }
    private static StatusCode? FindStatus(Exception? ex)
    {
        for (; ex is not null; ex = ex.InnerException)
            if (ex is ServiceResultException sre) return sre.StatusCode;
        return null;
    }
    [Fact]
@@ -93,7 +179,7 @@ public sealed class NatPublishedEndpointBrowseTests
        var ct = TestContext.Current.CancellationToken;
        await AssertAdvertisesUnreachableAddressAsync(endpoint, ct);
-        await using var session = await new OpcUaClientDriverBrowser().OpenAsync(Json(endpoint), ct);
+        await using var session = await Browser().OpenAsync(Json(endpoint), ct);
        var roots = await session.RootAsync(ct);
        roots.Count.ShouldBeGreaterThan(0);
@@ -111,7 +197,7 @@ public sealed class NatPublishedEndpointBrowseTests
        var ct = TestContext.Current.CancellationToken;
        // A closed loopback port: the rewrite must not invent a reachable address; the open fails promptly.
        var sw = System.Diagnostics.Stopwatch.StartNew();
-        await Should.ThrowAsync<Exception>(() => new OpcUaClientDriverBrowser().OpenAsync(Json("opc.tcp://127.0.0.1:1"), ct));
+        await Should.ThrowAsync<Exception>(() => Browser().OpenAsync(Json("opc.tcp://127.0.0.1:1"), ct));
        sw.Elapsed.ShouldBeLessThan(TimeSpan.FromSeconds(30));
    }
@@ -122,29 +208,59 @@ public sealed class NatPublishedEndpointBrowseTests
        var ct = TestContext.Current.CancellationToken;
        await AssertAdvertisesUnreachableAddressAsync(endpoint, ct);
-        // Basic256Sha256/SignAndEncrypt through the published port. The browse PKI never auto-accepts, so unless the
+        // Basic256Sha256/SignAndEncrypt through the published port, on a browse PKI that trusts NOTHING (the browse
-        // operator trusted this fixture's certificate in the browse PKI (then set OPCUA_NAT_SERVER_CERT_TRUSTED=1) the
+        // never auto-accepts): the open must be refused on the certificate — which proves the session reached the
-        // open must be refused on the certificate — which proves the session reached the SERVER (no DNS failure on the
+        // SERVER (no DNS failure on the advertised host) and that the rewrite did not relax trust.
        // advertised host) and that the rewrite did not relax trust.
        var trusted = Environment.GetEnvironmentVariable("OPCUA_NAT_SERVER_CERT_TRUSTED") == "1";
        var json = Json(endpoint, "Basic256Sha256", "SignAndEncrypt");
        if (trusted)
        {
            await using var session = await new OpcUaClientDriverBrowser().OpenAsync(json, ct);
            (await session.RootAsync(ct)).Count.ShouldBeGreaterThan(0);
            return;
        }
        var ex = await Should.ThrowAsync<Exception>(async () =>
        {
-            await using var session = await new OpcUaClientDriverBrowser().OpenAsync(json, ct);
+            await using var session = await Browser().OpenAsync(Json(endpoint, "Basic256Sha256", "SignAndEncrypt"), ct);
        });
        TestContext.Current.TestOutputHelper?.WriteLine($"secure open refused: {ex.GetType().Name}: {ex.Message}");
        ex.ShouldNotBeOfType<SocketException>($"must not fail on DNS for the advertised host: {ex}");
-        var sre = ex as ServiceResultException ?? ex.InnerException as ServiceResultException;
+        var status = FindStatus(ex);
-        sre.ShouldNotBeNull($"expected a certificate refusal, got {ex.GetType().Name}: {ex.Message}");
+        status.ShouldNotBeNull($"expected a certificate refusal, got {ex.GetType().Name}: {ex.Message}");
-        sre.StatusCode.ShouldBeOneOf(
+        status.Value.ShouldBeOneOf(
            StatusCodes.BadCertificateUntrusted, StatusCodes.BadSecurityChecksFailed,
            StatusCodes.BadCertificateChainIncomplete);
    }
    /// <summary>
    ///     #818 — the positive secure case, runnable in CI. #816 — with the host-name check unset (the default) or
    ///     explicitly off, a trusted certificate is accepted although it names <c>*-nat-private.invalid</c> and the
    ///     browse dialled the published address: the NAT opt-out.
    /// </summary>
    [Theory]
    [InlineData(null)]
    [InlineData(false)]
    public async Task Secure_browse_with_the_fixture_certificate_trusted_succeeds_without_a_host_name_check(bool? validate)
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        TrustFixtureCertificate(await AssertAdvertisesUnreachableAddressAsync(endpoint, ct));
        await using var session = await Browser().OpenAsync(
            Json(endpoint, "Basic256Sha256", "SignAndEncrypt", validate), ct);
        (await session.RootAsync(ct)).Count.ShouldBeGreaterThan(0);
    }
    /// <summary>
    ///     #816 — with the host-name check on, the SAME trusted certificate is refused, and the host checked is the one
    ///     the operator configured (the published address), not the server-advertised private name the certificate lists.
    /// </summary>
    [Fact]
    public async Task Host_name_validation_checks_the_configured_host_and_refuses_the_NAT_certificate()
    {
        var endpoint = RequireFixture();
        var ct = TestContext.Current.CancellationToken;
        TrustFixtureCertificate(await AssertAdvertisesUnreachableAddressAsync(endpoint, ct));
        var ex = await Should.ThrowAsync<Exception>(async () =>
        {
            await using var session = await Browser().OpenAsync(
                Json(endpoint, "Basic256Sha256", "SignAndEncrypt", validateHostName: true), ct);
        });
        TestContext.Current.TestOutputHelper?.WriteLine($"secure open refused: {ex.GetType().Name}: {ex.Message}");
        FindStatus(ex).ShouldBe(StatusCodes.BadCertificateHostNameInvalid, $"expected a host-name refusal, got {ex}");
        ex.ToString().ShouldContain($"'{new Uri(endpoint).IdnHost}'");
    }
 }
@@ -24,4 +24,11 @@
        <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj" />
    </ItemGroup>
    <ItemGroup>
        <!-- #818: the shared-host NAT fixture's PUBLIC server certificate (its PKI is on a persistent volume), trusted by
             NatPublishedEndpointBrowseTests in a throwaway browse PKI. Never a private key. -->
        <None Include="..\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests\Docker\nat\opc-plc-nat-server.der"
              Link="opc-plc-nat-server.der" CopyToOutputDirectory="PreserveNewest" />
    </ItemGroup>
 </Project>
@@ -10,7 +10,8 @@ here since opc-plc ships pre-containerized.
 | File | Purpose |
 |---|---|
 | [`docker-compose.yml`](docker-compose.yml) | Service definition for `otopcua-opc-plc` — image pin, port map, command flags. |
-| [`nat/docker-compose.yml`](nat/docker-compose.yml) | `otopcua-opc-plc-nat` — a SEPARATE stack (`/opt/otopcua-opcuaclient-nat` on the shared host): opc-plc advertising a private `.invalid` host on internal port 50000, published on 50010. For `NatPublishedEndpointBrowseTests` (`OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010`, #806/#813); see the compose file's header. |
+| [`nat/docker-compose.yml`](nat/docker-compose.yml) | `otopcua-opc-plc-nat` — a SEPARATE stack (`/opt/otopcua-opcuaclient-nat` on the shared host): opc-plc advertising a private `.invalid` host on internal port 50000, published on 50010. For `NatPublishedEndpointBrowseTests` (`OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010`, #806/#813); see the compose file's header. Its PKI is on a volume (#818). |
 | [`nat/opc-plc-nat-server.der`](nat/opc-plc-nat-server.der) | The NAT stack's **public** server certificate (no key), trusted by the positive secure / host-name NAT tests in a throwaway browse PKI. Refresh it when the stack's certificate is rolled (`docker compose down -v`); expires 2027-11-10. |
 | (this file) | How to run it. |
 ## Install
@@ -34,7 +35,8 @@ docker compose up
 ```
 First run pulls the image (~250 MB). Startup takes ~5-10 seconds; the
-healthcheck in the compose file surfaces ready state in `docker ps`.
+healthcheck in the compose file surfaces ready state in `docker ps` (a bash `/dev/tcp` probe —
 the image has no `netstat`, which kept the old check permanently "unhealthy", #817).
 To run detached (CI pattern):
@@ -20,6 +20,16 @@
 #   ssh dohertj2@10.100.0.35 'cd /opt/otopcua-opcuaclient-nat && docker compose up -d'
 #   OPCUA_NAT_ENDPOINT=opc.tcp://10.100.0.35:50010 dotnet test \
 #       tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.IntegrationTests --filter Fixture=opc-plc-nat
 #
 # #818: the server's PKI (/app/pki — own cert + private key, and the client certs --aa accepted) lives in the
 # named volume `opc-plc-nat-pki`, so recreating the container keeps the SAME server certificate. Its PUBLIC half is
 # committed next to this file (opc-plc-nat-server.der) and the secure tests trust it in a throwaway browse PKI. The
 # private key never leaves the volume. To roll the certificate deliberately (e.g. at expiry, 2027-11-10):
 #   ssh dohertj2@10.100.0.35 'cd /opt/otopcua-opcuaclient-nat && docker compose down -v && docker compose up -d'
 #   ssh dohertj2@10.100.0.35 'docker exec otopcua-opc-plc-nat bash -c "cat /app/pki/own/certs/*.der"' \
 #       > tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests/Docker/nat/opc-plc-nat-server.der
 # (until the committed copy is refreshed the positive secure tests SKIP on a thumbprint mismatch — they never pass
 # against a certificate other than the committed one).
 services:
  opc-plc-nat:
    image: mcr.microsoft.com/iotedge/opc-plc:2.14.10
@@ -40,11 +50,20 @@ services:
      # --aa: accept the browser's self-signed client cert. Trust in the OTHER direction (the browser trusting
      #       this server's cert) is deliberately not automatic — that is what the secure test pins.
      - "--aa"
    volumes:
      - opc-plc-nat-pki:/app/pki
    # The image runs as uid 1654 ("app") and ships no /app/pki, so Docker creates the volume mount point root-owned
    # and opc-plc could not write its certificate there. A throwaway test simulator: run it as root rather than add a
    # chown init container.
    user: "0"
    healthcheck:
-      # The image ships no netstat (the sibling ../docker-compose.yml healthcheck is permanently "unhealthy" for that
+      # The image ships no netstat (the sibling ../docker-compose.yml healthcheck was permanently "unhealthy" for that
-      # reason); bash's /dev/tcp is there.
+      # reason until #817 switched it to this probe too); bash's /dev/tcp is there.
      test: ["CMD", "bash", "-c", "exec 3<>/dev/tcp/127.0.0.1/50000"]
      interval: 5s
      timeout: 2s
      retries: 10
      start_period: 10s
 volumes:
  opc-plc-nat-pki:
@@ -0,0 +1,108 @@
 using Opc.Ua;
 using Shouldly;
 using Xunit;
 namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.IntegrationTests;
 /// <summary>
 ///     Gitea #816 — does the driver check the server certificate's host name? Against the plain opc-plc fixture, whose
 ///     certificate names only its container hostname (e.g. <c>DNS:1fc1de3fcb21</c>) while the driver dials the docker
 ///     host's address, so a host check MUST fail if it runs at all.
 ///     <para>Before #816 the driver called the SDK's 8-argument <c>DefaultSessionFactory.CreateAsync</c>, which hard-codes
 ///     <c>checkDomain: false</c>: the mismatch was never noticed. Now <c>certificateValidation.validateServerHostName</c>
 ///     decides; unset keeps the old behaviour.</para>
 ///     <para>Each test trusts the server's certificate in a THROWAWAY PKI (the driver's <c>PkiRootOverride</c>) with
 ///     auto-accept OFF — auto-accept also accepts a host-name mismatch and would hide the check. The certificate is
 ///     taken from the server's own GetEndpoints answer: what is under test is the host check, not how trust was
 ///     established.</para>
 /// </summary>
 [Collection(OpcPlcCollection.Name)]
 [Trait("Category", "Integration")]
 [Trait("Simulator", "opc-plc")]
 public sealed class ServerHostNameValidationTests(OpcPlcFixture sim) : IDisposable
 {
    private readonly string _pkiRoot = Path.Combine(Path.GetTempPath(), "otopcua-816-" + Guid.NewGuid().ToString("N"));
    /// <inheritdoc />
    public void Dispose()
    {
        try { Directory.Delete(_pkiRoot, recursive: true); } catch { /* best-effort temp cleanup */ }
    }
    private OpcUaClientDriverOptions SecureOptions(bool? validateHostName) => OpcPlcProfile.BuildOptions(sim.EndpointUrl) with
    {
        SecurityPolicy = OpcUaSecurityPolicy.Basic256Sha256,
        SecurityMode = OpcUaSecurityMode.SignAndEncrypt,
        AutoAcceptCertificates = false,
        CertificateValidation = new OpcUaCertificateValidationOptions { ValidateServerHostName = validateHostName },
    };
    /// <summary>Trust the fixture's server certificate (as advertised on its secure endpoint) in the throwaway PKI.</summary>
    private async Task TrustServerCertificateAsync(CancellationToken ct)
    {
        var appConfig = new ApplicationConfiguration(DefaultTelemetry.Create(_ => { }))
        {
            ApplicationName = "OtOpcUa #816 trust",
            ApplicationType = ApplicationType.Client,
            SecurityConfiguration = new SecurityConfiguration(),
            TransportQuotas = new TransportQuotas(),
            ClientConfiguration = new ClientConfiguration(),
            DisableHiResClock = true,
        };
        using var discovery = await DiscoveryClient.CreateAsync(appConfig, new Uri(sim.EndpointUrl), DiagnosticsMasks.None, ct);
        var endpoints = await discovery.GetEndpointsAsync(default, ct);
        var secure = endpoints.ToList().First(e => e.SecurityPolicyUri == SecurityPolicies.Basic256Sha256);
        var der = secure.ServerCertificate.ToArray();
        der.ShouldNotBeEmpty("the secure endpoint must carry the server certificate");
        var certs = Path.Combine(_pkiRoot, "trusted", "certs");
        Directory.CreateDirectory(certs);
        await File.WriteAllBytesAsync(Path.Combine(certs, "opc-plc.der"), der, ct);
    }
    private async Task<OpcUaClientDriver> InitializeAsync(bool? validateHostName, string id, CancellationToken ct)
    {
        var drv = new OpcUaClientDriver(SecureOptions(validateHostName), driverInstanceId: id) { PkiRootOverride = _pkiRoot };
        try
        {
            await drv.InitializeAsync("{}", ct);
            return drv;
        }
        catch
        {
            await drv.DisposeAsync();
            throw;
        }
    }
    [Theory]
    [InlineData(null)]   // unset = the pre-#816 behaviour every existing deployment has
    [InlineData(false)]  // the explicit NAT / IP-addressed opt-out
    public async Task Without_host_name_validation_a_trusted_certificate_for_another_host_connects(bool? validate)
    {
        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
        var ct = TestContext.Current.CancellationToken;
        await TrustServerCertificateAsync(ct);
        await using var drv = await InitializeAsync(validate, $"opcua-816-off-{validate}", ct);
        var snapshots = await drv.ReadAsync([OpcPlcProfile.StepUpRef], ct);
        snapshots[0].StatusCode.ShouldBe(0u, "the secured session must read once the server certificate is trusted");
    }
    [Fact]
    public async Task With_host_name_validation_the_certificate_is_checked_against_the_configured_host()
    {
        if (sim.SkipReason is not null) Assert.Skip(sim.SkipReason);
        var ct = TestContext.Current.CancellationToken;
        await TrustServerCertificateAsync(ct);
        var ex = await Should.ThrowAsync<Exception>(() => InitializeAsync(true, "opcua-816-on", ct));
        TestContext.Current.TestOutputHelper?.WriteLine($"refused: {ex}");
        // The driver's failover aggregate keeps per-endpoint failures as text. The SDK message names the host it
        // checked: the CONFIGURED one (the endpoint URL was rewritten to it), not whatever the server advertised.
        var configuredHost = new Uri(sim.EndpointUrl).IdnHost;
        var text = ex.ToString();
        text.ShouldContain($"The domain '{configuredHost}' is not listed in the server certificate");
        text.ShouldContain("validateServerHostName=false", Case.Sensitive, "the refusal must name the opt-out");
    }
 }
@@ -0,0 +1,57 @@
 using Opc.Ua;
 using Shouldly;
 using Xunit;
 namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;
 /// <summary>
 ///     Gitea #816 — <c>certificateValidation.validateServerHostName</c>. The wire behaviour (the SDK's checkDomain against
 ///     the CONFIGURED host) is pinned against real servers by <c>ServerHostNameValidationTests</c> (driver, plain opc-plc)
 ///     and <c>NatPublishedEndpointBrowseTests</c> (browser, NAT opc-plc); these pin the option contract.
 /// </summary>
 [Trait("Category", "Unit")]
 public sealed class OpcUaClientServerHostNameOptionTests
 {
    [Fact]
    public void Unset_resolves_to_off_so_existing_deployments_are_unchanged()
    {
        var o = new OpcUaClientDriverOptions();
        o.CertificateValidation.ValidateServerHostName.ShouldBeNull();
        o.CertificateValidation.EffectiveValidateServerHostName.ShouldBeFalse();
        OpcUaCertificateValidationOptions.DefaultValidateServerHostName.ShouldBeFalse();
        OpcUaClientDriverFactoryExtensions.ParseOptions("d", """{"endpointUrl":"opc.tcp://x:1"}""")
            .CertificateValidation.EffectiveValidateServerHostName.ShouldBeFalse();
    }
    [Theory]
    [InlineData("true", true)]
    [InlineData("false", false)]
    public void Factory_json_binds_the_explicit_choice(string json, bool expected)
    {
        var o = OpcUaClientDriverFactoryExtensions.ParseOptions("d",
            $$$"""{"endpointUrl":"opc.tcp://x:1","certificateValidation":{"validateServerHostName":{{{json}}}}}""");
        o.CertificateValidation.ValidateServerHostName.ShouldBe(expected);
        o.CertificateValidation.EffectiveValidateServerHostName.ShouldBe(expected);
    }
    [Fact]
    public void The_effective_value_is_not_serialised_back()
    {
        var json = System.Text.Json.JsonSerializer.Serialize(new OpcUaCertificateValidationOptions());
        json.ShouldNotContain("Effective");
    }
    [Fact]
    public void A_host_name_refusal_names_the_opt_out()
    {
        var hint = OpcUaClientDriver.HostNameRefusalHint(new ServiceResultException(
            StatusCodes.BadCertificateHostNameInvalid, "The domain '10.1.2.3' is not listed in the server certificate."));
        hint.ShouldContain("validateServerHostName=false");
        OpcUaClientDriver.HostNameRefusalHint(new ServiceResultException(StatusCodes.BadCertificateUntrusted))
            .ShouldBeEmpty();
        OpcUaClientDriver.HostNameRefusalHint(new InvalidOperationException("x")).ShouldBeEmpty();
    }
 }
@@ -180,6 +180,31 @@ public sealed class OpcUaClientDriverPageFormSerializationTests
        def.DiscoveryUrl.ShouldBeNull();
    }
    /// <summary>
    ///     #816: the server host-name check is tri-state. Unset must stay unset through the form (so a later change of
    ///     the driver default reaches configs nobody chose for), and an explicit opt-in / NAT opt-out must survive.
    /// </summary>
    [Theory]
    [InlineData(null)]
    [InlineData(true)]
    [InlineData(false)]
    public void FormModel_RoundTrip_PreservesHostNameValidationTriState(bool? value)
    {
        var formOpts = new JsonSerializerOptions(_opts) { Converters = { new JsonStringEnumConverter() } };
        var original = new OpcUaClientDriverOptions
        {
            CertificateValidation = new OpcUaCertificateValidationOptions { ValidateServerHostName = value },
        };
        var back = OpcUaClientDriverForm.OpcUaClientFormModel.FromRecord(original).ToRecord([]);
        back.CertificateValidation.ValidateServerHostName.ShouldBe(value);
        var reparsed = JsonSerializer.Deserialize<OpcUaClientDriverOptions>(
            JsonSerializer.Serialize(back, formOpts), formOpts)!;
        reparsed.CertificateValidation.ValidateServerHostName.ShouldBe(value);
        reparsed.CertificateValidation.EffectiveValidateServerHostName.ShouldBe(value ?? false);
    }
    /// <summary>
    ///     #648: stored DriverConfig JSON from before <c>targetNamespaceKind</c>/<c>unsMappingTable</c> were removed
    ///     must still load into the form (the form's options use <c>UnmappedMemberHandling.Skip</c>) and the legacy