diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Configuration/TelemetryStreamAuthInterceptor.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Configuration/TelemetryStreamAuthInterceptor.cs
new file mode 100644
index 00000000..7f331c7b
--- /dev/null
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Configuration/TelemetryStreamAuthInterceptor.cs
@@ -0,0 +1,165 @@
+using System.Security.Cryptography;
+using System.Text;
+using Grpc.Core;
+using Grpc.Core.Interceptors;
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using ZB.MOM.WW.OtOpcUa.Cluster;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Configuration;
+
+///
+/// Gates the driver-node telemetry stream endpoint (per-cluster mesh Phase 5). The
+/// TelemetryStreamService.Subscribe RPC streams a node's live alerts / script-logs /
+/// driver-health / driver-resilience-status to whoever dials it; anything able to reach a driver
+/// node's telemetry port could otherwise pull that live feed out-of-band. This interceptor is the
+/// ONLY inbound auth on that endpoint.
+///
+///
+///
+/// Scoped by method path. Only calls under
+/// /telemetry.v1.TelemetryStreamService/ are gated; every other method on the shared
+/// gRPC pipeline (config-serve, LocalDb sync) passes through untouched, so this can share one
+/// AddGrpc registration with and
+/// .
+///
+///
+/// Fail-closed. With no Telemetry:ApiKey configured, NO dial is accepted,
+/// authenticated or not. Treating "no key" as "no auth required" would expose the live
+/// telemetry feed on exactly the default shape most nodes ship with. The caller dialing in
+/// must present the same TelemetryDial:ApiKey (the shared node key), so a key typo
+/// stops telemetry delivery outright rather than degrading to unauthenticated.
+///
+///
+/// Comparison is over UTF-8 bytes, so a
+/// wrong key cannot be recovered byte-by-byte from response timing. Length differences are
+/// unavoidably observable and are not sensitive.
+///
+///
+/// Exactly one public constructor. Grpc.AspNetCore silently stops invoking an
+/// interceptor that has more than one public ctor — see
+/// TelemetryStreamAuthInterceptorTests.HasExactlyOnePublicConstructor.
+///
+///
+public sealed class TelemetryStreamAuthInterceptor : Interceptor
+{
+ private const string ServicePrefix = "/telemetry.v1.TelemetryStreamService/";
+ private const string AuthorizationHeader = "authorization";
+ private const string BearerPrefix = "Bearer ";
+
+ private readonly IOptions _options;
+ private readonly ILogger _logger;
+
+ /// Creates the interceptor.
+ /// Telemetry options; ApiKey is the expected bearer token.
+ /// Logger for denial diagnostics.
+ public TelemetryStreamAuthInterceptor(
+ IOptions options,
+ ILogger logger)
+ {
+ ArgumentNullException.ThrowIfNull(options);
+ ArgumentNullException.ThrowIfNull(logger);
+
+ _options = options;
+ _logger = logger;
+ }
+
+ ///
+ public override Task UnaryServerHandler(
+ TRequest request,
+ ServerCallContext context,
+ UnaryServerMethod continuation)
+ {
+ Authorize(context);
+ return continuation(request, context);
+ }
+
+ ///
+ public override Task DuplexStreamingServerHandler(
+ IAsyncStreamReader requestStream,
+ IServerStreamWriter responseStream,
+ ServerCallContext context,
+ DuplexStreamingServerMethod continuation)
+ {
+ Authorize(context);
+ return continuation(requestStream, responseStream, context);
+ }
+
+ ///
+ public override Task ClientStreamingServerHandler(
+ IAsyncStreamReader requestStream,
+ ServerCallContext context,
+ ClientStreamingServerMethod continuation)
+ {
+ Authorize(context);
+ return continuation(requestStream, context);
+ }
+
+ ///
+ public override Task ServerStreamingServerHandler(
+ TRequest request,
+ IServerStreamWriter responseStream,
+ ServerCallContext context,
+ ServerStreamingServerMethod continuation)
+ {
+ Authorize(context);
+ return continuation(request, responseStream, context);
+ }
+
+ ///
+ /// Throws with if this is
+ /// a telemetry-stream call that does not carry the configured bearer token. Non-telemetry
+ /// calls return immediately.
+ ///
+ private void Authorize(ServerCallContext context)
+ {
+ if (!context.Method.StartsWith(ServicePrefix, StringComparison.Ordinal))
+ return;
+
+ var expected = _options.Value.ApiKey;
+ if (string.IsNullOrEmpty(expected))
+ {
+ _logger.LogWarning(
+ "Rejected a telemetry stream call to {Method}: no Telemetry:ApiKey is configured, so " +
+ "the telemetry endpoint is closed. Configure the shared node key on this node and every " +
+ "dialing caller.",
+ context.Method);
+ throw new RpcException(new Status(
+ StatusCode.PermissionDenied,
+ "Telemetry stream is not accepting connections: no API key is configured on this node."));
+ }
+
+ var presented = ExtractBearerToken(context.RequestHeaders);
+ if (presented is null || !FixedTimeEquals(presented, expected))
+ {
+ _logger.LogWarning(
+ "Rejected a telemetry stream call to {Method}: {Reason}.",
+ context.Method,
+ presented is null ? "no bearer token presented" : "bearer token did not match");
+ throw new RpcException(new Status(
+ StatusCode.PermissionDenied,
+ "Telemetry stream authentication failed."));
+ }
+ }
+
+ private static string? ExtractBearerToken(Metadata headers)
+ {
+ // gRPC lowercases header keys on the wire; compare case-insensitively anyway so a hand-built
+ // Metadata in a test behaves the same as a real request.
+ foreach (var entry in headers)
+ {
+ if (!string.Equals(entry.Key, AuthorizationHeader, StringComparison.OrdinalIgnoreCase))
+ continue;
+
+ var value = entry.Value;
+ if (value is not null && value.StartsWith(BearerPrefix, StringComparison.OrdinalIgnoreCase))
+ return value[BearerPrefix.Length..];
+ }
+
+ return null;
+ }
+
+ private static bool FixedTimeEquals(string presented, string expected)
+ => CryptographicOperations.FixedTimeEquals(
+ Encoding.UTF8.GetBytes(presented), Encoding.UTF8.GetBytes(expected));
+}
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/Configuration/TelemetryStreamAuthInterceptorTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/Configuration/TelemetryStreamAuthInterceptorTests.cs
new file mode 100644
index 00000000..287945d7
--- /dev/null
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.Host.Tests/Configuration/TelemetryStreamAuthInterceptorTests.cs
@@ -0,0 +1,199 @@
+using Grpc.Core;
+using Microsoft.Extensions.Logging.Abstractions;
+using Microsoft.Extensions.Options;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Cluster;
+using ZB.MOM.WW.OtOpcUa.Host.Configuration;
+
+namespace ZB.MOM.WW.OtOpcUa.Host.Tests.Configuration;
+
+///
+/// Per-cluster mesh Phase 5 — the telemetry stream endpoint's inbound gate. Wiring this
+/// interceptor into the AddGrpc pipeline + Kestrel is a separate, later task; this test
+/// covers only the interceptor's own authorization behavior.
+///
+///
+/// Same contract as / ,
+/// scoped to /telemetry.v1.TelemetryStreamService/ — fail-closed on an unconfigured key,
+/// constant-time comparison, gated on every handler shape so scoping holds regardless of RPC shape.
+///
+public sealed class TelemetryStreamAuthInterceptorTests
+{
+ private const string SubscribeMethod = "/telemetry.v1.TelemetryStreamService/Subscribe";
+ private const string OtherMethod = "/deployment_artifact.v1.DeploymentArtifactService/Fetch";
+
+ private static TelemetryStreamAuthInterceptor CreateInterceptor(string? apiKey)
+ => new(
+ Options.Create(new TelemetryOptions { ApiKey = apiKey ?? string.Empty }),
+ NullLogger.Instance);
+
+ private static ServerCallContext CreateContext(string method, string? authorizationHeader)
+ {
+ var headers = new Metadata();
+ if (authorizationHeader is not null)
+ headers.Add("authorization", authorizationHeader);
+
+ return new FakeServerCallContext(method, headers);
+ }
+
+ /// Invokes the interceptor's server-streaming path (how Subscribe actually runs).
+ private static Task Invoke(TelemetryStreamAuthInterceptor interceptor, ServerCallContext context)
+ => interceptor.ServerStreamingServerHandler(
+ "request", responseStream: null!, context, (_, _, _) => Task.CompletedTask);
+
+ [Fact]
+ public async Task NonTelemetryMethod_PassesThrough_EvenWithNoKeyConfigured()
+ {
+ // The interceptor shares the AddGrpc pipeline with other gRPC services, so it sees every
+ // call. It must be scoped strictly to the telemetry service.
+ var interceptor = CreateInterceptor(apiKey: null);
+ var context = CreateContext(OtherMethod, authorizationHeader: null);
+
+ await Invoke(interceptor, context); // no throw
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_WithNoKeyConfigured_IsDenied_EvenWithABearerToken()
+ {
+ // Fail-closed. "No key configured" is the DEFAULT — treating it as "no auth required" would
+ // expose live telemetry on exactly the shape most nodes ship with. A token must not help.
+ var interceptor = CreateInterceptor(apiKey: null);
+ var context = CreateContext(SubscribeMethod, "Bearer anything-at-all");
+
+ var ex = await Should.ThrowAsync(() => Invoke(interceptor, context));
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_WithNoBearerToken_IsDenied()
+ {
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, authorizationHeader: null);
+
+ var ex = await Should.ThrowAsync(() => Invoke(interceptor, context));
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_WithMalformedAuthorizationHeader_IsDenied()
+ {
+ // No "Bearer " prefix at all — must be treated the same as a missing header.
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "the-shared-key");
+
+ var ex = await Should.ThrowAsync(() => Invoke(interceptor, context));
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_WithWrongBearerToken_IsDenied()
+ {
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-wrong-key");
+
+ var ex = await Should.ThrowAsync(() => Invoke(interceptor, context));
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_WithCorrectBearerToken_PassesThrough()
+ {
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-shared-key");
+
+ await Invoke(interceptor, context); // no throw
+ }
+
+ [Fact]
+ public async Task SubscribeMethod_TokenComparison_IsNotAPrefixMatch()
+ {
+ // A prefix/StartsWith comparison would accept a truncated key and make the secret
+ // recoverable one character at a time.
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-shared-ke");
+
+ var ex = await Should.ThrowAsync(() => Invoke(interceptor, context));
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task UnaryPath_IsAlsoGated()
+ {
+ // Subscribe is server-streaming today, but gating only that path would leave any future
+ // unary method on the same service open. Gate every handler shape.
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-wrong-key");
+
+ var ex = await Should.ThrowAsync(() =>
+ interceptor.UnaryServerHandler(
+ "request", context, (_, _) => Task.FromResult("ok")));
+
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task ClientStreamingPath_IsAlsoGated()
+ {
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-wrong-key");
+
+ var ex = await Should.ThrowAsync(() =>
+ interceptor.ClientStreamingServerHandler(
+ requestStream: null!, context, (_, _) => Task.FromResult("ok")));
+
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public async Task DuplexStreamingPath_IsAlsoGated()
+ {
+ var interceptor = CreateInterceptor("the-shared-key");
+ var context = CreateContext(SubscribeMethod, "Bearer the-wrong-key");
+
+ var ex = await Should.ThrowAsync(() =>
+ interceptor.DuplexStreamingServerHandler(
+ requestStream: null!, responseStream: null!, context, (_, _, _) => Task.CompletedTask));
+
+ ex.StatusCode.ShouldBe(StatusCode.PermissionDenied);
+ }
+
+ [Fact]
+ public void HasExactlyOnePublicConstructor()
+ {
+ // Grpc.AspNetCore silently stops invoking an interceptor with more than one public ctor —
+ // this pins the shape so a well-meaning overload doesn't quietly disable auth in production.
+ var publicCtors = typeof(TelemetryStreamAuthInterceptor).GetConstructors();
+
+ publicCtors.Length.ShouldBe(1);
+ }
+
+ ///
+ /// Minimal carrying just a method name and request headers —
+ /// the only two things the interceptor reads. Hand-rolled because
+ /// Grpc.Core.Testing.TestServerCallContext ships only in the retired native package.
+ ///
+ private sealed class FakeServerCallContext(string method, Metadata requestHeaders)
+ : ServerCallContext
+ {
+ protected override string MethodCore => method;
+ protected override string HostCore => "localhost";
+ protected override string PeerCore => "ipv4:127.0.0.1:12345";
+ protected override DateTime DeadlineCore => DateTime.UtcNow.AddMinutes(1);
+ protected override Metadata RequestHeadersCore => requestHeaders;
+ protected override CancellationToken CancellationTokenCore => CancellationToken.None;
+ protected override Metadata ResponseTrailersCore { get; } = [];
+ protected override Status StatusCore { get; set; }
+ protected override WriteOptions? WriteOptionsCore { get; set; }
+
+ protected override AuthContext AuthContextCore { get; } =
+ new(null, new Dictionary>());
+
+ protected override ContextPropagationToken CreatePropagationTokenCore(
+ ContextPropagationOptions? options)
+ => throw new NotSupportedException();
+
+ protected override Task WriteResponseHeadersAsyncCore(Metadata responseHeaders)
+ => Task.CompletedTask;
+ }
+}