diff --git a/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/Internal/LdapUserName.cs b/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/Internal/LdapUserName.cs
index 8c500a6..0d03e8a 100644
--- a/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/Internal/LdapUserName.cs
+++ b/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/Internal/LdapUserName.cs
@@ -2,8 +2,11 @@ namespace ZB.MOM.WW.Auth.Ldap.Internal;
 
 /// <summary>
 /// Reduces a typed login to the bare account name used by <see cref="Abstractions.Ldap.LdapBindMode.User"/>:
-/// one spelling flows into the bind template, the search filter and the returned username, so audit
-/// rows never carry <c>DOMAIN\jdoe</c> for one sign-in and <c>jdoe</c> for the next.
+/// the qualifier is stripped before the name reaches the bind template and the search filter, so audit
+/// rows never carry <c>DOMAIN\jdoe</c> for one sign-in and <c>jdoe</c> for the next. Case is NOT
+/// normalised here: the returned username is canonicalised from the directory entry's
+/// <c>UserNameAttribute</c> value, so <c>JDoe</c> and <c>jdoe</c> also yield one identity; this name is
+/// only the fallback when the entry has no such value.
 /// </summary>
 internal static class LdapUserName
 {
diff --git a/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/LdapAuthService.cs b/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/LdapAuthService.cs
index 676cbd6..927edd8 100644
--- a/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/LdapAuthService.cs
+++ b/ZB.MOM.WW.Auth/src/ZB.MOM.WW.Auth.Ldap/LdapAuthService.cs
@@ -145,16 +145,19 @@ public sealed class LdapAuthService : ILdapAuthService
         //    filter and the returned result (avoids two identities for one person).
         username = username.Trim();
 
-        // 3b. User-bind mode guards, before any network call. An empty password must never reach
-        //     the directory: AD answers a simple bind with an empty password as an UNAUTHENTICATED
-        //     bind and reports success, which would admit anyone. The name is reduced to the bare
-        //     account name so the bind template, the search filter and the result share one spelling.
-        if (_options.BindMode == LdapBindMode.User)
+        // 3b. An empty password must never reach the directory, in EITHER bind mode: AD answers a
+        //     simple bind with an empty password as an UNAUTHENTICATED bind and reports success —
+        //     the user bind (or the ServiceAccount-mode re-bind as the user's DN) would admit anyone.
+        //     Refused here, before any network call, so no consumer depends on its own edge check.
+        if (string.IsNullOrEmpty(password))
+            return LdapAuthResult.Fail(LdapAuthFailure.BadCredentials);
+
+        // 3c. User-bind mode: reduce the name to the bare account name the bind template and the
+        //     search filter share. (The returned username is canonicalised from the entry later.)
+        if (_options.BindMode == LdapBindMode.User
+            && !LdapUserName.TryNormalize(username, _options.AcceptDomainQualifiedNames, out username))
         {
-            if (string.IsNullOrEmpty(password))
-                return LdapAuthResult.Fail(LdapAuthFailure.BadCredentials);
-            if (!LdapUserName.TryNormalize(username, _options.AcceptDomainQualifiedNames, out username))
-                return LdapAuthResult.Fail(LdapAuthFailure.BadCredentials);
+            return LdapAuthResult.Fail(LdapAuthFailure.BadCredentials);
         }
 
         // 4. Walk the endpoint list, preferred one first. A single-endpoint configuration
@@ -278,7 +281,8 @@ public sealed class LdapAuthService : ILdapAuthService
     private LdapAuthResult CompleteWithServiceAccount(ZB.MOM.WW.Auth.Ldap.Internal.ILdapConnection conn, string username, string password)
     {
         // 6. Service-account bind so we can search for the user's DN. A bind failure here is a
-        //    service-account misconfiguration — DISTINCT from a user-credential failure.
+        //    service-account misconfiguration — DISTINCT from a user-credential failure — so it
+        //    maps to ServiceAccountBindFailed.
         try
         {
             conn.Bind(_options.ServiceAccountDn, _options.ServiceAccountPassword);
@@ -288,7 +292,9 @@ public sealed class LdapAuthService : ILdapAuthService
             throw new StageFailure(LdapAuthFailure.ServiceAccountBindFailed, "service-bind");
         }
 
-        // 7–8. Exactly one match. Zero -> UserNotFound; two or more -> AmbiguousUser.
+        // 7–8. Require exactly one match. Zero -> UserNotFound; two or more -> AmbiguousUser.
+        //      Both are authoritative answers from a healthy directory, so they end the walk.
+        //      We never attempt a user bind against an ambiguous DN.
         var entries = SearchUser(conn, username);
         if (entries.Count == 0)
             return LdapAuthResult.Fail(LdapAuthFailure.UserNotFound);
@@ -297,7 +303,9 @@ public sealed class LdapAuthService : ILdapAuthService
 
         var entry = entries[0];
 
-        // 9. User bind verifies the password; a failure is the user's bad credentials and final.
+        // 9. User bind: re-bind as the resolved DN to verify the password. A bind failure here is
+        //    the end user's bad credentials — the directory answered, so this is returned directly
+        //    and never retried against another endpoint.
         try
         {
             conn.Bind(entry.Dn, password);
@@ -344,6 +352,10 @@ public sealed class LdapAuthService : ILdapAuthService
     /// <summary>Step 7: search for the user entry; a search fault is system-side.</summary>
     private IReadOnlyList<LdapSearchEntry> SearchUser(ZB.MOM.WW.Auth.Ldap.Internal.ILdapConnection conn, string username)
     {
+        // A search failure is infrastructure (directory unreachable / unhealthy) — system-side.
+        // NOTE: the LdapAuthFailure enum has no DirectoryUnavailable value, so a failed search maps
+        //       to ServiceAccountBindFailed, the closest system-side bucket (same limitation as
+        //       Connect), until a DirectoryUnavailable value exists.
         try
         {
             var filter = $"({_options.UserNameAttribute}={LdapEscaping.Filter(username)})";
@@ -355,7 +367,12 @@ public sealed class LdapAuthService : ILdapAuthService
         }
     }
 
-    /// <summary>Steps 10–11: fail-closed group extraction, then success.</summary>
+    /// <summary>
+    /// Steps 10–11: fail-closed group extraction, then success. The returned username is the
+    /// entry's own <see cref="LdapOptions.UserNameAttribute"/> value (the directory's spelling), so
+    /// <c>JDoe</c> and <c>jdoe</c> sign in as one identity; the typed (normalised) name is the
+    /// fallback when the entry carries no such value.
+    /// </summary>
     private LdapAuthResult SucceedFromEntry(LdapSearchEntry entry, string username)
     {
         IReadOnlyList<string> groups;
@@ -371,7 +388,8 @@ public sealed class LdapAuthService : ILdapAuthService
         if (groups.Count == 0)
             return LdapAuthResult.Fail(LdapAuthFailure.GroupLookupFailed);
 
-        return LdapAuthResult.Success(username, ExtractDisplayName(entry, username), groups);
+        var canonical = ExtractUserName(entry, username);
+        return LdapAuthResult.Success(canonical, ExtractDisplayName(entry, canonical), groups);
     }
 
     /// <summary>
@@ -393,16 +411,37 @@ public sealed class LdapAuthService : ILdapAuthService
     }
 
     /// <summary>
-    /// Builds the distinct attribute list requested from the directory. The display-name
-    /// and group attributes are de-duplicated so we never request the same attribute twice
-    /// when an operator configures them to the same value.
+    /// Builds the distinct attribute list requested from the directory: display name, groups and
+    /// the username attribute (read back as the canonical username). They are de-duplicated,
+    /// case-insensitively, so we never request the same attribute twice when an operator
+    /// configures two of them to the same value.
     /// </summary>
     private IReadOnlyList<string> BuildSearchAttributes()
     {
-        if (string.Equals(_options.DisplayNameAttribute, _options.GroupAttribute, StringComparison.OrdinalIgnoreCase))
-            return new[] { _options.DisplayNameAttribute };
+        var attributes = new List<string>(3);
+        foreach (var name in new[] { _options.DisplayNameAttribute, _options.GroupAttribute, _options.UserNameAttribute })
+        {
+            if (!attributes.Contains(name, StringComparer.OrdinalIgnoreCase))
+                attributes.Add(name);
+        }
 
-        return new[] { _options.DisplayNameAttribute, _options.GroupAttribute };
+        return attributes;
+    }
+
+    /// <summary>
+    /// Returns the first non-blank value of the configured username attribute — the directory's
+    /// canonical spelling — falling back to the (already normalised) typed username.
+    /// </summary>
+    private string ExtractUserName(LdapSearchEntry entry, string username)
+    {
+        if (entry.Attributes.TryGetValue(_options.UserNameAttribute, out var values)
+            && values.Count > 0
+            && !string.IsNullOrWhiteSpace(values[0]))
+        {
+            return values[0];
+        }
+
+        return username;
     }
 
     /// <summary>
diff --git a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/FakeLdapConnection.cs b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/FakeLdapConnection.cs
index ddb3e23..5075200 100644
--- a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/FakeLdapConnection.cs
+++ b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/FakeLdapConnection.cs
@@ -34,6 +34,9 @@ internal sealed class FakeLdapConnection : ILdapConnection
     /// </summary>
     public int BindAttempts { get; private set; }
 
+    /// <summary>The attribute list passed to the most recent <see cref="Search"/> call (the fake still returns every scripted attribute).</summary>
+    public IReadOnlyList<string>? SearchAttributes { get; private set; }
+
     /// <summary>Every call in order: <c>connect</c>, <c>bind:&lt;dn&gt;</c>, <c>search:&lt;filter&gt;</c>.</summary>
     public List<string> Calls { get; } = new();
 
@@ -41,9 +44,14 @@ internal sealed class FakeLdapConnection : ILdapConnection
 
     /// <summary>
     /// Scripts a user entry that will be returned by the next <see cref="Search"/> call.
-    /// Builds a minimal attribute bag with <c>memberOf</c> and optional <c>displayName</c>.
+    /// Builds a minimal attribute bag with <c>memberOf</c>, optional <c>displayName</c> and any
+    /// <paramref name="extraAttributes"/> (e.g. <c>sAMAccountName</c>) the test needs.
     /// </summary>
-    public FakeLdapConnection WithUserEntry(string dn, string[] memberOf, string? displayName = null)
+    public FakeLdapConnection WithUserEntry(
+        string dn,
+        string[] memberOf,
+        string? displayName = null,
+        IReadOnlyDictionary<string, string[]>? extraAttributes = null)
     {
         var attrs = new Dictionary<string, IReadOnlyList<string>>(StringComparer.OrdinalIgnoreCase)
         {
@@ -51,6 +59,11 @@ internal sealed class FakeLdapConnection : ILdapConnection
         };
         if (displayName is not null)
             attrs["displayName"] = new[] { displayName };
+        if (extraAttributes is not null)
+        {
+            foreach (var (name, values) in extraAttributes)
+                attrs[name] = values;
+        }
 
         _scriptedEntries.Add(new LdapSearchEntry(dn, attrs));
         return this;
@@ -177,6 +190,7 @@ internal sealed class FakeLdapConnection : ILdapConnection
         IReadOnlyList<string> attributes)
     {
         Calls.Add($"search:{filter}");
+        SearchAttributes = attributes;
         if (_throwOnSearch)
             throw new Novell.Directory.Ldap.LdapException(
                 "Search failed", Novell.Directory.Ldap.LdapException.Unavailable, searchBase);
diff --git a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceTests.cs b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceTests.cs
index 44ff334..91d54d4 100644
--- a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceTests.cs
+++ b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceTests.cs
@@ -147,4 +147,45 @@ public class LdapAuthServiceTests
         Assert.True(r.Succeeded);
         Assert.Equal(new[] { "Eng,ineers", "A,B" }, r.Groups);
     }
+
+    [Fact]
+    public async Task Username_IsCanonicalisedFromTheEntry_InServiceAccountMode()
+    {
+        var fake = new FakeLdapConnection().WithUserEntry(
+            "cn=alice,dc=x", new[] { "cn=g,dc=x" }, "Alice",
+            new Dictionary<string, string[]> { ["cn"] = new[] { "alice" } });
+        var svc = new LdapAuthService(Opts(), new FakeLdapConnectionFactory(fake));
+
+        var r = await svc.AuthenticateAsync("ALICE", "pw", default);
+
+        Assert.True(r.Succeeded);
+        Assert.Equal("alice", r.Username);
+    }
+
+    [Fact]
+    public async Task Username_FallsBackToTheTypedName_InServiceAccountMode_WhenAttributeAbsent()
+    {
+        var fake = new FakeLdapConnection().WithUserEntry("cn=alice,dc=x", new[] { "cn=g,dc=x" }, "Alice");
+        var svc = new LdapAuthService(Opts(), new FakeLdapConnectionFactory(fake));
+
+        var r = await svc.AuthenticateAsync("ALICE", "pw", default);
+
+        Assert.True(r.Succeeded);
+        Assert.Equal("ALICE", r.Username);
+    }
+
+    [Theory]
+    [InlineData("")]
+    [InlineData(null)]
+    public async Task EmptyPassword_IsRefused_InServiceAccountMode_WithoutContactingTheDirectory(string? password)
+    {
+        var factory = new SequenceLdapConnectionFactory(
+            new FakeLdapConnection().WithUserEntry("cn=alice,dc=x", new[] { "cn=g,dc=x" }, "Alice"));
+        var svc = new LdapAuthService(Opts(), factory);
+
+        var r = await svc.AuthenticateAsync("alice", password!, default);
+
+        Assert.Equal(LdapAuthFailure.BadCredentials, r.Failure);
+        Assert.Empty(factory.Created);
+    }
 }
diff --git a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceUserBindTests.cs b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceUserBindTests.cs
index 1276c1a..7350867 100644
--- a/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceUserBindTests.cs
+++ b/ZB.MOM.WW.Auth/tests/ZB.MOM.WW.Auth.Ldap.Tests/LdapAuthServiceUserBindTests.cs
@@ -178,4 +178,45 @@ public class LdapAuthServiceUserBindTests
 
         Assert.Equal(LdapAuthFailure.GroupLookupFailed, result.Failure);
     }
+
+    [Fact]
+    public async Task Username_IsCanonicalisedFromTheEntry_NotTheTypedCase()
+    {
+        var factory = new SequenceLdapConnectionFactory(new FakeLdapConnection().WithUserEntry(
+            "CN=Jane Doe,OU=u,DC=x", new[] { "CN=UG_A,OU=g,DC=x" }, "Jane Doe",
+            new Dictionary<string, string[]> { ["sAMAccountName"] = new[] { "jdoe" } }));
+        var result = await Login(new LdapAuthService(Opts(), factory), @"NAM\JDOE");
+
+        Assert.True(result.Succeeded);
+        Assert.Equal("jdoe", result.Username);
+    }
+
+    [Fact]
+    public async Task Username_FallsBackToTheTypedName_WhenTheEntryLacksTheAttribute()
+    {
+        var factory = new SequenceLdapConnectionFactory(Jane());
+        var result = await Login(new LdapAuthService(Opts(), factory), "JDOE");
+
+        Assert.True(result.Succeeded);
+        Assert.Equal("JDOE", result.Username);
+    }
+
+    [Fact]
+    public async Task Search_RequestsTheUserNameAttribute()
+    {
+        var factory = new SequenceLdapConnectionFactory(Jane());
+        await Login(new LdapAuthService(Opts(), factory), "jdoe");
+
+        Assert.Equal(new[] { "displayName", "memberOf", "sAMAccountName" }, factory.Created[0].SearchAttributes);
+    }
+
+    [Fact]
+    public async Task Search_DeDuplicatesTheUserNameAttribute_CaseInsensitively()
+    {
+        var factory = new SequenceLdapConnectionFactory(Jane());
+        var svc = new LdapAuthService(Opts() with { DisplayNameAttribute = "SAMACCOUNTNAME" }, factory);
+        await Login(svc, "jdoe");
+
+        Assert.Equal(new[] { "SAMACCOUNTNAME", "memberOf" }, factory.Created[0].SearchAttributes);
+    }
 }