diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
index faba0946..15180c94 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Certificates/CertificateStoreManager.cs
@@ -1,6 +1,8 @@
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
 using Microsoft.Extensions.Configuration;
+using ZB.MOM.WW.Audit;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Audit;
 
 namespace ZB.MOM.WW.OtOpcUa.AdminUI.Certificates;
 
@@ -25,31 +27,61 @@ public sealed class CertificateStoreManager
         new(StringComparer.OrdinalIgnoreCase) { "trusted", "rejected" };
 
     private readonly string _pkiRoot;
+    private readonly IAuditWriter _audit;
 
     /// <summary>Production ctor — reads <c>OpcUa:PkiStoreRoot</c> (default <c>pki</c>).</summary>
     /// <param name="config">App configuration.</param>
-    public CertificateStoreManager(IConfiguration config)
-        => _pkiRoot = config.GetValue<string?>("OpcUa:PkiStoreRoot") ?? "pki";
+    /// <param name="audit">The audit writer that persists Trust/Untrust/Delete actions to <c>ConfigAuditLog</c>.</param>
+    public CertificateStoreManager(IConfiguration config, IAuditWriter audit)
+    {
+        _pkiRoot = config.GetValue<string?>("OpcUa:PkiStoreRoot") ?? "pki";
+        _audit = audit;
+    }
 
     /// <summary>Test ctor — explicit PKI root.</summary>
     /// <param name="pkiRoot">The PKI store root directory.</param>
-    internal CertificateStoreManager(string pkiRoot) => _pkiRoot = pkiRoot;
+    /// <param name="audit">Optional audit writer; defaults to a no-op writer when omitted.</param>
+    internal CertificateStoreManager(string pkiRoot, IAuditWriter? audit = null)
+    {
+        _pkiRoot = pkiRoot;
+        _audit = audit ?? NoOpAuditWriter.Instance;
+    }
 
     /// <summary>Moves a rejected peer cert into the trusted store.</summary>
     /// <param name="thumbprint">The cert thumbprint.</param>
+    /// <param name="actor">The identity performing the action; recorded in the audit log.</param>
     /// <returns>The action result.</returns>
-    public CertActionResult Trust(string thumbprint) => Move("rejected", "trusted", thumbprint);
+    public CertActionResult Trust(string thumbprint, string actor)
+    {
+        var r = Move("rejected", "trusted", thumbprint);
+        Audit("Trust", "rejected→trusted", thumbprint, actor, r);
+        return r;
+    }
 
     /// <summary>Moves a trusted peer cert back into the rejected store.</summary>
     /// <param name="thumbprint">The cert thumbprint.</param>
+    /// <param name="actor">The identity performing the action; recorded in the audit log.</param>
     /// <returns>The action result.</returns>
-    public CertActionResult Untrust(string thumbprint) => Move("trusted", "rejected", thumbprint);
+    public CertActionResult Untrust(string thumbprint, string actor)
+    {
+        var r = Move("trusted", "rejected", thumbprint);
+        Audit("Untrust", "trusted→rejected", thumbprint, actor, r);
+        return r;
+    }
 
     /// <summary>Deletes a cert from the named mutable store (<c>trusted</c> or <c>rejected</c>).</summary>
     /// <param name="store">The store name.</param>
     /// <param name="thumbprint">The cert thumbprint.</param>
+    /// <param name="actor">The identity performing the action; recorded in the audit log.</param>
     /// <returns>The action result.</returns>
-    public CertActionResult Delete(string store, string thumbprint)
+    public CertActionResult Delete(string store, string thumbprint, string actor)
+    {
+        var r = DeleteCore(store, thumbprint);
+        Audit("Delete", store, thumbprint, actor, r);
+        return r;
+    }
+
+    private CertActionResult DeleteCore(string store, string thumbprint)
     {
         if (!MutableStores.Contains(store)) return CertActionResult.Fail($"unknown store '{store}'");
         if (!IsValidThumbprint(thumbprint)) return CertActionResult.Fail("invalid thumbprint");
@@ -66,6 +98,12 @@ public sealed class CertificateStoreManager
         }
     }
 
+    // Fire-and-forget: the writer enqueues synchronously and returns a completed task, so the
+    // store mutation stays synchronous. Every return path (success + every failure) is audited
+    // because Trust/Untrust/Delete each route their single result through here.
+    private void Audit(string action, string store, string thumbprint, string actor, CertActionResult r)
+        => _audit.WriteAsync(CertAuditEvents.Build(action, store, thumbprint, actor, r.Success, r.Error));
+
     private CertActionResult Move(string fromSub, string toSub, string thumbprint)
     {
         if (!IsValidThumbprint(thumbprint)) return CertActionResult.Fail("invalid thumbprint");
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Certificates.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Certificates.razor
index b0be8210..3f2b6c25 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Certificates.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Pages/Certificates.razor
@@ -191,14 +191,15 @@ else
             return;
         }
 
+        var actor = authState.User.Identity?.Name ?? "system";
         var result = p.Verb switch
         {
-            "trust"   => CertManager.Trust(p.Thumbprint),
-            "untrust" => CertManager.Untrust(p.Thumbprint),
+            "trust"   => CertManager.Trust(p.Thumbprint, actor),
+            "untrust" => CertManager.Untrust(p.Thumbprint, actor),
             "delete"  => p.Kind switch
             {
-                StoreKind.Trusted  => CertManager.Delete("trusted", p.Thumbprint),
-                StoreKind.Rejected => CertManager.Delete("rejected", p.Thumbprint),
+                StoreKind.Trusted  => CertManager.Delete("trusted", p.Thumbprint, actor),
+                StoreKind.Rejected => CertManager.Delete("rejected", p.Thumbprint, actor),
                 _                  => CertActionResult.Fail($"cannot delete from {p.Kind}"),
             },
             _ => CertActionResult.Fail("unknown action"),
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
index 97b35ead..3e9ecd1b 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Certificates/CertificateStoreManagerTests.cs
@@ -9,12 +9,27 @@ namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Certificates;
 public sealed class CertificateStoreManagerTests : IDisposable
 {
     private readonly string _root;
+    private readonly RecordingAuditWriter _audit;
     private readonly CertificateStoreManager _sut;
 
     public CertificateStoreManagerTests()
     {
         _root = Path.Combine(Path.GetTempPath(), $"pki-test-{Guid.NewGuid():N}");
-        _sut = new CertificateStoreManager(_root);
+        _audit = new RecordingAuditWriter();
+        _sut = new CertificateStoreManager(_root, _audit);
+    }
+
+    // ── Recording audit-writer fake ───────────────────────────────────────────
+
+    private sealed class RecordingAuditWriter : ZB.MOM.WW.Audit.IAuditWriter
+    {
+        public List<ZB.MOM.WW.Audit.AuditEvent> Events { get; } = new();
+
+        public Task WriteAsync(ZB.MOM.WW.Audit.AuditEvent evt, CancellationToken ct = default)
+        {
+            Events.Add(evt);
+            return Task.CompletedTask;
+        }
     }
 
     public void Dispose()
@@ -84,7 +99,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var rejectedCerts = Path.Combine(_root, "rejected", "certs");
         var tp = SeedCert(rejectedCerts, "TestClient1");
 
-        var result = _sut.Trust(tp);
+        var result = _sut.Trust(tp, "tester");
 
         result.Success.ShouldBeTrue(result.Error);
         ThumbprintExistsInDir(rejectedCerts, tp).ShouldBeFalse("cert should have left rejected");
@@ -97,7 +112,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var trustedCerts = Path.Combine(_root, "trusted", "certs");
         var tp = SeedCert(trustedCerts, "TestClient2");
 
-        var result = _sut.Untrust(tp);
+        var result = _sut.Untrust(tp, "tester");
 
         result.Success.ShouldBeTrue(result.Error);
         ThumbprintExistsInDir(trustedCerts, tp).ShouldBeFalse("cert should have left trusted");
@@ -110,7 +125,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var rejectedCerts = Path.Combine(_root, "rejected", "certs");
         var tp = SeedCert(rejectedCerts, "TestClient3");
 
-        var result = _sut.Delete("rejected", tp);
+        var result = _sut.Delete("rejected", tp, "tester");
 
         result.Success.ShouldBeTrue(result.Error);
         ThumbprintExistsInDir(rejectedCerts, tp).ShouldBeFalse("cert should be gone from rejected");
@@ -122,7 +137,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var trustedCerts = Path.Combine(_root, "trusted", "certs");
         var tp = SeedCert(trustedCerts, "TestClient4");
 
-        var result = _sut.Delete("trusted", tp);
+        var result = _sut.Delete("trusted", tp, "tester");
 
         result.Success.ShouldBeTrue(result.Error);
         ThumbprintExistsInDir(trustedCerts, tp).ShouldBeFalse("cert should be gone from trusted");
@@ -133,7 +148,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
     {
         var tp = new string('A', 40);
 
-        var result = _sut.Trust(tp);
+        var result = _sut.Trust(tp, "tester");
 
         result.Success.ShouldBeFalse();
         CertCountInDir(Path.Combine(_root, "trusted", "certs")).ShouldBe(0);
@@ -142,7 +157,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
     [Fact]
     public void Trust_PathTraversalThumbprint_Rejected()
     {
-        var result = _sut.Trust("../../x");
+        var result = _sut.Trust("../../x", "tester");
 
         result.Success.ShouldBeFalse();
         result.Error.ShouldNotBeNull();
@@ -158,7 +173,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var ownCerts = Path.Combine(_root, "own", "certs");
         var tp = SeedCert(ownCerts, "OwnCert");
 
-        var result = _sut.Delete("own", tp);
+        var result = _sut.Delete("own", tp, "tester");
 
         result.Success.ShouldBeFalse();
         result.Error.ShouldNotBeNull();
@@ -178,7 +193,7 @@ public sealed class CertificateStoreManagerTests : IDisposable
         var srcFile = Directory.GetFiles(rejectedCerts).Single();
         File.Copy(srcFile, Path.Combine(trustedCerts, Path.GetFileName(srcFile)));
 
-        var result = _sut.Trust(tp);
+        var result = _sut.Trust(tp, "tester");
 
         result.Success.ShouldBeTrue(result.Error);
         ThumbprintExistsInDir(rejectedCerts, tp).ShouldBeFalse("source (rejected) should no longer have it");
@@ -188,9 +203,89 @@ public sealed class CertificateStoreManagerTests : IDisposable
     [Fact]
     public void Trust_NullOrEmptyThumbprint_Fails()
     {
-        var result = _sut.Trust("");
+        var result = _sut.Trust("", "tester");
 
         result.Success.ShouldBeFalse();
         result.Error.ShouldNotBeNull();
     }
+
+    // ── Audit tests ───────────────────────────────────────────────────────────
+
+    [Fact]
+    public void Trust_success_writes_one_success_audit_event()
+    {
+        var rejectedCerts = Path.Combine(_root, "rejected", "certs");
+        var tp = SeedCert(rejectedCerts, "AuditTrust");
+
+        var result = _sut.Trust(tp, "alice");
+
+        result.Success.ShouldBeTrue(result.Error);
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Trust");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Success);
+        evt.SourceNode.ShouldBe(tp);
+        evt.Actor.ShouldBe("alice");
+    }
+
+    [Fact]
+    public void Untrust_success_writes_one_success_audit_event()
+    {
+        var trustedCerts = Path.Combine(_root, "trusted", "certs");
+        var tp = SeedCert(trustedCerts, "AuditUntrust");
+
+        var result = _sut.Untrust(tp, "alice");
+
+        result.Success.ShouldBeTrue(result.Error);
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Untrust");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Success);
+        evt.SourceNode.ShouldBe(tp);
+        evt.Actor.ShouldBe("alice");
+    }
+
+    [Fact]
+    public void Delete_success_writes_one_success_audit_event()
+    {
+        var rejectedCerts = Path.Combine(_root, "rejected", "certs");
+        var tp = SeedCert(rejectedCerts, "AuditDelete");
+
+        var result = _sut.Delete("rejected", tp, "alice");
+
+        result.Success.ShouldBeTrue(result.Error);
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Delete");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Success);
+        evt.SourceNode.ShouldBe(tp);
+        evt.Actor.ShouldBe("alice");
+    }
+
+    [Fact]
+    public void Delete_not_found_writes_one_failure_audit_event()
+    {
+        var absent = new string('0', 40);
+
+        var result = _sut.Delete("trusted", absent, "bob");
+
+        result.Success.ShouldBeFalse();
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Delete");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Failure);
+        evt.SourceNode.ShouldBe(absent);
+        evt.Actor.ShouldBe("bob");
+    }
+
+    [Fact]
+    public void Trust_not_found_writes_one_failure_audit_event()
+    {
+        var absent = new string('0', 40);
+
+        var result = _sut.Trust(absent, "bob");
+
+        result.Success.ShouldBeFalse();
+        var evt = _audit.Events.ShouldHaveSingleItem();
+        evt.Action.ShouldBe("Trust");
+        evt.Outcome.ShouldBe(ZB.MOM.WW.Audit.AuditOutcome.Failure);
+        evt.SourceNode.ShouldBe(absent);
+        evt.Actor.ShouldBe("bob");
+    }
 }