diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAlarmSource.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAlarmSource.cs
index 09521fc6..ef967a28 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAlarmSource.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAlarmSource.cs
@@ -41,10 +41,15 @@ public interface IAlarmSubscriptionHandle
 }
 
 /// <summary>One alarm acknowledgement in a batch.</summary>
+/// <param name="SourceNodeId">Driver-side identifier for the alarm source.</param>
+/// <param name="ConditionId">Stable id correlating raise / ack / clear of the same condition.</param>
+/// <param name="Comment">Operator-supplied comment forwarded to the upstream alarm system.</param>
+/// <param name="OperatorUser">Authenticated principal performing the ack; null on the raw/non-OPC-UA path.</param>
 public sealed record AlarmAcknowledgeRequest(
     string SourceNodeId,
     string ConditionId,
-    string? Comment);
+    string? Comment,
+    string? OperatorUser = null);
 
 /// <summary>Event payload for <see cref="IAlarmSource.OnAlarmEvent"/>.</summary>
 /// <param name="SubscriptionHandle">Subscription this event belongs to.</param>
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmSource.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmSource.cs
index 684f1d55..eabf3411 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmSource.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms/ScriptedAlarmSource.cs
@@ -68,11 +68,11 @@ public sealed class ScriptedAlarmSource : IAlarmSource, IDisposable
         if (acknowledgements is null) throw new ArgumentNullException(nameof(acknowledgements));
         foreach (var a in acknowledgements)
         {
-            // The base interface doesn't carry a user identity — Stream G provides the
-            // authenticated principal at the OPC UA dispatch layer + proxies through
-            // the engine's richer AcknowledgeAsync. Here we default to "opcua-client"
-            // so callers using the raw IAlarmSource still produce an audit entry.
-            await _engine.AcknowledgeAsync(a.ConditionId, "opcua-client", a.Comment, cancellationToken)
+            // Honor the authenticated principal carried on the request when present
+            // (the OPC UA dispatch layer / Stream G threads it through). When absent —
+            // the raw/non-OPC-UA path — default to "opcua-client" so the ack still
+            // produces an audit entry.
+            await _engine.AcknowledgeAsync(a.ConditionId, a.OperatorUser ?? "opcua-client", a.Comment, cancellationToken)
                 .ConfigureAwait(false);
         }
     }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
index a3f098da..f7a7efbd 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/GalaxyDriver.cs
@@ -1122,7 +1122,9 @@ public sealed class GalaxyDriver
             await _alarmAcknowledger.AcknowledgeAsync(
                 alarmFullReference,
                 ack.Comment ?? string.Empty,
-                operatorUser: string.Empty, // server-side ACL fills this from the OPC UA session
+                // Honor the authenticated principal carried on the request when present;
+                // fall back to empty (server-side ACL fills this from the OPC UA session).
+                operatorUser: ack.OperatorUser ?? string.Empty,
                 cancellationToken).ConfigureAwait(false);
         }
     }
diff --git a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests/ScriptedAlarmSourceTests.cs b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests/ScriptedAlarmSourceTests.cs
index ce499c52..dda21ce5 100644
--- a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests/ScriptedAlarmSourceTests.cs
+++ b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.ScriptedAlarms.Tests/ScriptedAlarmSourceTests.cs
@@ -129,6 +129,37 @@ public sealed class ScriptedAlarmSourceTests
         state.LastAckComment.ShouldBe("ack via opcua");
     }
 
+    /// <summary>
+    ///     Verifies that AcknowledgeAsync honors a supplied authenticated principal
+    ///     (<see cref="AlarmAcknowledgeRequest.OperatorUser"/>) and falls back to
+    ///     <c>"opcua-client"</c> only when none is supplied.
+    /// </summary>
+    [Fact]
+    public async Task ScriptedAlarmSource_uses_supplied_principal_else_default()
+    {
+        var (engine, source, up) = await BuildAsync();
+        using var _e = engine;
+        using var _s = source;
+
+        // Supplied principal -> honored.
+        up.Push("Temp", 150);
+        await Task.Delay(200);
+        await source.AcknowledgeAsync([new AlarmAcknowledgeRequest(
+            "Plant/Line1", "Plant/Line1::HighTemp", "ack as bob", "bob")],
+            TestContext.Current.CancellationToken);
+        engine.GetState("Plant/Line1::HighTemp")!.LastAckUser.ShouldBe("bob");
+
+        // No principal -> default audit identity.
+        up.Push("Temp", 50);
+        await Task.Delay(200);
+        up.Push("Temp", 150);
+        await Task.Delay(200);
+        await source.AcknowledgeAsync([new AlarmAcknowledgeRequest(
+            "Plant/Line1", "Plant/Line1::HighTemp", "ack anon", null)],
+            TestContext.Current.CancellationToken);
+        engine.GetState("Plant/Line1::HighTemp")!.LastAckUser.ShouldBe("opcua-client");
+    }
+
     /// <summary>Verifies that null arguments are rejected.</summary>
     [Fact]
     public async Task Null_arguments_rejected()
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/GalaxyDriverAlarmSourceTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/GalaxyDriverAlarmSourceTests.cs
index 0a9c173e..dd523b0e 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/GalaxyDriverAlarmSourceTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Tests/GalaxyDriverAlarmSourceTests.cs
@@ -210,6 +210,26 @@ public sealed class GalaxyDriverAlarmSourceTests
         ack.Calls[0].AlarmRef.ShouldBe("Tank01.Level.HiHi");
     }
 
+    /// <summary>
+    ///     Verifies that AcknowledgeAsync forwards the request's authenticated principal
+    ///     (<see cref="AlarmAcknowledgeRequest.OperatorUser"/>) to the acknowledger so the
+    ///     gateway records WHO acked, rather than the generic empty-string fallback.
+    /// </summary>
+    [Fact]
+    public async Task AcknowledgeAsync_forwards_OperatorUser()
+    {
+        var feed = new FakeAlarmFeed();
+        var ack = new RecordingAcknowledger();
+        using var driver = NewDriver(feed, ack);
+
+        await driver.AcknowledgeAsync(
+            [new AlarmAcknowledgeRequest("src", "Obj.Alarm", "cmt", "alice")],
+            CancellationToken.None);
+
+        ack.Calls.ShouldHaveSingleItem();
+        ack.Calls[0].Operator.ShouldBe("alice");
+    }
+
     /// <summary>Verifies that AcknowledgeAsync throws NotSupportedException without an acknowledger.</summary>
     [Fact]
     public async Task AcknowledgeAsync_throws_NotSupported_without_acknowledger()