diff --git a/src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/ForwardedAuthenticationTests.cs b/src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/ForwardedAuthenticationTests.cs
new file mode 100644
index 000000000..120f621d9
--- /dev/null
+++ b/src/EventStore.Core.Tests/Services/Transport/Grpc/StreamsTests/ForwardedAuthenticationTests.cs
@@ -0,0 +1,141 @@
+using System;
+using System.Collections.Generic;
+using System.Reflection;
+using System.Security.Claims;
+using System.Threading;
+using System.Threading.Tasks;
+using EventStore.Client.Streams;
+using EventStore.Core.Authorization;
+using EventStore.Core.Bus;
+using EventStore.Core.Messages;
+using EventStore.Core.Messaging;
+using EventStore.Core.Services.Transport.Grpc;
+using Google.Protobuf;
+using Grpc.Core;
+using Microsoft.AspNetCore.Http;
+using NUnit.Framework;
+using GrpcMetadata = EventStore.Core.Services.Transport.Grpc.Constants.Metadata;
+using GrpcStreams = EventStore.Client.Streams.Streams;
+
+namespace EventStore.Core.Tests.Services.Transport.Grpc.StreamsTests;
+
+[TestFixture]
+public class ForwardedAuthenticationTests
+{
+	[Test]
+	public void append_reports_forwarded_authentication_failure()
+	{
+		var service = CreateService(new AuthenticationFailurePublisher());
+		var requests = new EnumerableStreamReader<AppendReq>([
+			new AppendReq {
+				Options = new AppendReq.Types.Options {
+					NoStream = new(),
+					StreamIdentifier = "forwarded-auth-append"
+				}
+			},
+			new AppendReq {
+				ProposedMessage = new AppendReq.Types.ProposedMessage {
+					Id = Uuid.NewUuid().ToDto(),
+					Metadata = {
+						[GrpcMetadata.Type] = "test",
+						[GrpcMetadata.ContentType] = GrpcMetadata.ContentTypes.ApplicationJson
+					},
+					Data = ByteString.CopyFromUtf8("{}")
+				}
+			}
+		]);
+
+		var exception = Assert.ThrowsAsync<RpcException>(() => service.Append(requests, new TestServerCallContext()));
+
+		Assert.That(exception!.StatusCode, Is.EqualTo(StatusCode.Unauthenticated));
+		Assert.That(exception.Status.Detail, Does.Contain("forwarding denied"));
+	}
+
+	[Test]
+	public void delete_reports_forwarded_authentication_failure()
+	{
+		var service = CreateService(new AuthenticationFailurePublisher());
+		var request = new DeleteReq
+		{
+			Options = new DeleteReq.Types.Options
+			{
+				NoStream = new(),
+				StreamIdentifier = "forwarded-auth-delete"
+			}
+		};
+
+		var exception = Assert.ThrowsAsync<RpcException>(() => service.Delete(request, new TestServerCallContext()));
+
+		Assert.That(exception!.StatusCode, Is.EqualTo(StatusCode.Unauthenticated));
+		Assert.That(exception.Status.Detail, Does.Contain("forwarding denied"));
+	}
+
+	private static GrpcStreams.StreamsBase CreateService(IPublisher publisher)
+	{
+		var type = typeof(GrpcTrackers).Assembly.GetType(
+			"EventStore.Core.Services.Transport.Grpc.Streams`1", throwOnError: true)!
+			.MakeGenericType(typeof(string));
+		return (GrpcStreams.StreamsBase)Activator.CreateInstance(type,
+			BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
+			binder: null,
+			args: [publisher, 1024, TimeSpan.FromSeconds(1), null, new GrpcTrackers(), new PassthroughAuthorizationProvider()],
+			culture: null)!;
+	}
+
+	private sealed class AuthenticationFailurePublisher : IPublisher
+	{
+		public void Publish(Message message)
+		{
+			if (message is not ClientMessage.WriteRequestMessage request)
+			{
+				throw new InvalidOperationException($"Unexpected message {message.GetType().Name}");
+			}
+
+			request.Envelope.ReplyWith(new ClientMessage.NotAuthenticated(request.CorrelationId, "forwarding denied"));
+		}
+	}
+
+	private sealed class EnumerableStreamReader<T>(IEnumerable<T> values) : IAsyncStreamReader<T>
+	{
+		private readonly IEnumerator<T> _values = values.GetEnumerator();
+		public T Current { get; private set; } = default!;
+
+		public Task<bool> MoveNext(CancellationToken cancellationToken)
+		{
+			if (!_values.MoveNext())
+			{
+				return Task.FromResult(false);
+			}
+
+			Current = _values.Current;
+			return Task.FromResult(true);
+		}
+	}
+
+	private sealed class TestServerCallContext : ServerCallContext
+	{
+		public TestServerCallContext()
+		{
+			UserStateCore["__HttpContext"] = new DefaultHttpContext
+			{
+				User = new ClaimsPrincipal(new ClaimsIdentity())
+			};
+		}
+
+		protected override string MethodCore => "/event_store.client.streams.Streams/Append";
+		protected override string HostCore => "localhost";
+		protected override string PeerCore => "ipv4:127.0.0.1:2113";
+		protected override DateTime DeadlineCore => DateTime.MaxValue;
+		protected override Metadata RequestHeadersCore { get; } = new();
+		protected override CancellationToken CancellationTokenCore => CancellationToken.None;
+		protected override Metadata ResponseTrailersCore { get; } = new();
+		protected override Status StatusCore { get; set; }
+		protected override WriteOptions WriteOptionsCore { get; set; }
+		protected override AuthContext AuthContextCore { get; } =
+			new(string.Empty, new Dictionary<string, List<AuthProperty>>());
+		protected override IDictionary<object, object> UserStateCore { get; } = new Dictionary<object, object>();
+		protected override Task WriteResponseHeadersAsyncCore(Metadata responseHeaders) => Task.CompletedTask;
+		protected override ContextPropagationToken CreatePropagationTokenCore(ContextPropagationOptions options) =>
+			throw new NotSupportedException();
+	}
+}
diff --git a/src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs b/src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs
index ddff83de3..3cc40c215 100644
--- a/src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs
+++ b/src/EventStore.Core/Services/Transport/Grpc/Streams.Append.cs
@@ -122,6 +122,12 @@ void HandleWriteEventsCompleted(Message message)
 						appendResponseSource.TrySetException(ex);
 						return;
 					}
+					if (message is ClientMessage.NotAuthenticated notAuthenticated)
+					{
+						appendResponseSource.TrySetException(new RpcException(
+							new Status(StatusCode.Unauthenticated, notAuthenticated.Reason)));
+						return;
+					}
 
 					if (!(message is ClientMessage.WriteEventsCompleted completed))
 					{
diff --git a/src/EventStore.Core/Services/Transport/Grpc/Streams.Delete.cs b/src/EventStore.Core/Services/Transport/Grpc/Streams.Delete.cs
index c798b152c..bd0a441ed 100644
--- a/src/EventStore.Core/Services/Transport/Grpc/Streams.Delete.cs
+++ b/src/EventStore.Core/Services/Transport/Grpc/Streams.Delete.cs
@@ -148,6 +148,12 @@ void HandleStreamDeletedCompleted(Message message)
 				deleteResponseSource.TrySetException(ex);
 				return;
 			}
+			if (message is ClientMessage.NotAuthenticated notAuthenticated)
+			{
+				deleteResponseSource.TrySetException(new RpcException(
+					new Status(StatusCode.Unauthenticated, notAuthenticated.Reason)));
+				return;
+			}
 
 			if (message is not ClientMessage.DeleteStreamCompleted completed)
 			{