Phase 6.2 Stream C (foundation) — AuthorizationGate + ILdapGroupsBearer

Lands the integration seam between the Server project's OPC UA stack and the
Core.Authorization evaluator. Actual DriverNodeManager dispatch-path wiring
(Read/Write/HistoryRead/Browse/Call/Subscribe/Alarm surfaces) lands in the
follow-up PR on this branch — covered by Task #143 below.

Server.Security additions:
- ILdapGroupsBearer — marker interface a custom IUserIdentity implements to
  expose its resolved LDAP group DNs. Parallel to the existing IRoleBearer
  (admin roles) — control/data-plane separation per decision #150.
- AuthorizationGate — stateless bridge between Opc.Ua.IUserIdentity and
  IPermissionEvaluator. IsAllowed(identity, operation, scope) materializes a
  UserAuthorizationState from the identity's LDAP groups, delegates to the
  evaluator, and returns a single bool the dispatch paths use to decide
  whether to surface BadUserAccessDenied.
- StrictMode knob controls fail-open-during-transition vs fail-closed:
  - strict=false (default during rollout) — null identity, identity without
    ILdapGroupsBearer, or NotGranted outcome all return true so older
    deployments without ACL data keep working.
  - strict=true (production target) — any of the above returns false.
  The appsetting `Authorization:StrictMode = true` flips deployments over
  once their ACL data is populated.

Tests (9 new in Server.Tests/AuthorizationGateTests):
- Null identity — strict denies, lax allows.
- Identity without LDAP groups — strict denies, lax allows.
- LDAP group with matching grant allows.
- LDAP group without grant — strict denies.
- Wrong operation denied (Read-only grant, WriteOperate requested).
- BuildSessionState returns materialized state with LDAP groups + null when
  identity doesn't carry them.

Full solution dotnet test: 1087 passing (Phase 6.1 = 1042, Phase 6.2 A = +9,
B = +27, C foundation = +9 = 1087). Pre-existing Client.CLI Subscribe flake
unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/OpcUaOperation.cs

@@ -0,0 +1,59 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+/// <summary>
+///     Every OPC UA operation surface the Phase 6.2 authorization evaluator gates, per
+///     <c>docs/v2/implementation/phase-6-2-authorization-runtime.md</c> §Stream C and
+///     decision #143. The evaluator maps each operation onto the corresponding
+///     <c>NodePermissions</c> bit(s) to decide whether the calling session is allowed.
+/// </summary>
+/// <remarks>
+///     Write is split out into <see cref="WriteOperate"/> / <see cref="WriteTune"/> /
+///     <see cref="WriteConfigure"/> because the underlying driver-reported
+///     <see cref="SecurityClassification"/> already carries that distinction — the
+///     evaluator maps the requested tag's security class to the matching operation value
+///     before checking the permission bit.
+/// </remarks>
+public enum OpcUaOperation
+{
+    /// <summary>
+    ///     <c>Browse</c> + <c>TranslateBrowsePathsToNodeIds</c>. Ancestor visibility implied
+    ///     when any descendant has a grant; denied ancestors filter from browse results.
+    /// </summary>
+    Browse,
+
+    /// <summary><c>Read</c> on a variable node.</summary>
+    Read,
+
+    /// <summary><c>Write</c> when the target has <see cref="SecurityClassification.Operate"/> / <see cref="SecurityClassification.FreeAccess"/>.</summary>
+    WriteOperate,
+
+    /// <summary><c>Write</c> when the target has <see cref="SecurityClassification.Tune"/>.</summary>
+    WriteTune,
+
+    /// <summary><c>Write</c> when the target has <see cref="SecurityClassification.Configure"/>.</summary>
+    WriteConfigure,
+
+    /// <summary><c>HistoryRead</c> — uses its own <c>NodePermissions.HistoryRead</c> bit; Read alone is NOT sufficient (decision in Phase 6.2 Compliance).</summary>
+    HistoryRead,
+
+    /// <summary><c>HistoryUpdate</c> — annotation / insert / delete on historian.</summary>
+    HistoryUpdate,
+
+    /// <summary><c>CreateMonitoredItems</c>. Per-item denial in mixed-authorization batches.</summary>
+    CreateMonitoredItems,
+
+    /// <summary><c>TransferSubscriptions</c>. Re-evaluates transferred items against current auth state.</summary>
+    TransferSubscriptions,
+
+    /// <summary><c>Call</c> on a Method node.</summary>
+    Call,
+
+    /// <summary>Alarm <c>Acknowledge</c>.</summary>
+    AlarmAcknowledge,
+
+    /// <summary>Alarm <c>Confirm</c>.</summary>
+    AlarmConfirm,
+
+    /// <summary>Alarm <c>Shelve</c> / <c>Unshelve</c>.</summary>
+    AlarmShelve,
+}

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/AuthorizationDecision.cs

@@ -0,0 +1,48 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Tri-state result of an <see cref="IPermissionEvaluator.Authorize"/> call, per decision
+///     #149. Phase 6.2 only produces <see cref="AuthorizationVerdict.Allow"/> and
+///     <see cref="AuthorizationVerdict.NotGranted"/>; the <see cref="AuthorizationVerdict.Denied"/>
+///     variant exists in the model so v2.1 Explicit Deny lands without an API break. Provenance
+///     carries the matched grants (or empty when not granted) for audit + the Admin UI "Probe
+///     this permission" diagnostic.
+/// </summary>
+public sealed record AuthorizationDecision(
+    AuthorizationVerdict Verdict,
+    IReadOnlyList<MatchedGrant> Provenance)
+{
+    public bool IsAllowed => Verdict == AuthorizationVerdict.Allow;
+
+    /// <summary>Convenience constructor for the common "no grants matched" outcome.</summary>
+    public static AuthorizationDecision NotGranted() => new(AuthorizationVerdict.NotGranted, []);
+
+    /// <summary>Allow with the list of grants that matched.</summary>
+    public static AuthorizationDecision Allowed(IReadOnlyList<MatchedGrant> provenance)
+        => new(AuthorizationVerdict.Allow, provenance);
+}
+
+/// <summary>Three-valued authorization outcome.</summary>
+public enum AuthorizationVerdict
+{
+    /// <summary>At least one grant matches the requested (operation, scope) pair.</summary>
+    Allow,
+
+    /// <summary>No grant matches. Phase 6.2 default — treated as deny at the OPC UA surface.</summary>
+    NotGranted,
+
+    /// <summary>Explicit deny grant matched. Reserved for v2.1; never produced by Phase 6.2.</summary>
+    Denied,
+}
+
+/// <summary>One grant that contributed to an Allow verdict — for audit / UI diagnostics.</summary>
+/// <param name="LdapGroup">LDAP group the matched grant belongs to.</param>
+/// <param name="Scope">Where in the hierarchy the grant was anchored.</param>
+/// <param name="PermissionFlags">The bitmask the grant contributed.</param>
+public sealed record MatchedGrant(
+    string LdapGroup,
+    NodeAclScopeKind Scope,
+    NodePermissions PermissionFlags);

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/IPermissionEvaluator.cs

@@ -0,0 +1,23 @@
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Evaluates whether a session is authorized to perform an OPC UA <see cref="OpcUaOperation"/>
+///     on the node addressed by a <see cref="NodeScope"/>. Phase 6.2 Stream B central surface.
+/// </summary>
+/// <remarks>
+///     Data-plane only. Reads <c>NodeAcl</c> rows joined against the session's resolved LDAP
+///     groups (via <see cref="UserAuthorizationState"/>). Must not depend on
+///     <c>LdapGroupRoleMapping</c> (control-plane) per decision #150.
+/// </remarks>
+public interface IPermissionEvaluator
+{
+    /// <summary>
+    ///     Authorize the requested operation for the session. Callers (<c>DriverNodeManager</c>
+    ///     Read / Write / HistoryRead / Subscribe / Browse / Call dispatch) map their native
+    ///     failure to <c>BadUserAccessDenied</c> per OPC UA Part 4 when the result is not
+    ///     <see cref="AuthorizationVerdict.Allow"/>.
+    /// </summary>
+    AuthorizationDecision Authorize(UserAuthorizationState session, OpcUaOperation operation, NodeScope scope);
+}

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/NodeScope.cs

@@ -0,0 +1,58 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Address of a node in the 6-level scope hierarchy the Phase 6.2 evaluator walks.
+///     Assembled by the dispatch layer from the node's namespace + UNS path + tag; passed
+///     to <see cref="IPermissionEvaluator"/> which walks the matching trie path.
+/// </summary>
+/// <remarks>
+///     <para>Per decision #129 and the Phase 6.2 Stream B plan the hierarchy is
+///     <c>Cluster → Namespace → UnsArea → UnsLine → Equipment → Tag</c> for UNS
+///     (Equipment-kind) namespaces. Galaxy (SystemPlatform-kind) namespaces instead use
+///     <c>Cluster → Namespace → FolderSegment(s) → Tag</c>, and each folder segment takes
+///     one trie level — so a deeply-nested Galaxy folder implicitly reaches the same
+///     depth as a full UNS path.</para>
+///
+///     <para>Unset mid-path levels (e.g. a Cluster-scoped request with no UnsArea) leave
+///     the corresponding id <c>null</c>. The evaluator walks as far as the scope goes +
+///     stops at the first null.</para>
+/// </remarks>
+public sealed record NodeScope
+{
+    /// <summary>Cluster the node belongs to. Required.</summary>
+    public required string ClusterId { get; init; }
+
+    /// <summary>Namespace within the cluster. Null is not allowed for a request against a real node.</summary>
+    public string? NamespaceId { get; init; }
+
+    /// <summary>For Equipment-kind namespaces: UNS area (e.g. "warsaw-west"). Null on Galaxy.</summary>
+    public string? UnsAreaId { get; init; }
+
+    /// <summary>For Equipment-kind namespaces: UNS line below the area. Null on Galaxy.</summary>
+    public string? UnsLineId { get; init; }
+
+    /// <summary>For Equipment-kind namespaces: equipment row below the line. Null on Galaxy.</summary>
+    public string? EquipmentId { get; init; }
+
+    /// <summary>
+    ///     For Galaxy (SystemPlatform-kind) namespaces only: the folder path segments from
+    ///     namespace root to the target tag, in order. Empty on Equipment namespaces.
+    /// </summary>
+    public IReadOnlyList<string> FolderSegments { get; init; } = [];
+
+    /// <summary>Target tag id when the scope addresses a specific tag; null for folder / equipment-level scopes.</summary>
+    public string? TagId { get; init; }
+
+    /// <summary>Which hierarchy applies — Equipment-kind (UNS) or SystemPlatform-kind (Galaxy).</summary>
+    public required NodeHierarchyKind Kind { get; init; }
+}
+
+/// <summary>Selector between the two scope-hierarchy shapes.</summary>
+public enum NodeHierarchyKind
+{
+    /// <summary><c>Cluster → Namespace → UnsArea → UnsLine → Equipment → Tag</c> — UNS / Equipment kind.</summary>
+    Equipment,
+
+    /// <summary><c>Cluster → Namespace → FolderSegment(s) → Tag</c> — Galaxy / SystemPlatform kind.</summary>
+    SystemPlatform,
+}

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/PermissionTrie.cs

@@ -0,0 +1,125 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     In-memory permission trie for one <c>(ClusterId, GenerationId)</c>. Walk from the cluster
+///     root down through namespace → UNS levels (or folder segments) → tag, OR-ing the
+///     <see cref="TrieGrant.PermissionFlags"/> granted at each visited level for each of the session's
+///     LDAP groups. The accumulated bitmask is compared to the permission required by the
+///     requested <see cref="Abstractions.OpcUaOperation"/>.
+/// </summary>
+/// <remarks>
+///     Per decision #129 (additive grants, no explicit Deny in v2.0) the walk is pure union:
+///     encountering a grant at any level contributes its flags, never revokes them. A grant at
+///     the Cluster root therefore cascades to every tag below it; a grant at a deep equipment
+///     leaf is visible only on that equipment subtree.
+/// </remarks>
+public sealed class PermissionTrie
+{
+    /// <summary>Cluster this trie belongs to.</summary>
+    public required string ClusterId { get; init; }
+
+    /// <summary>Config generation the trie was built from — used by the cache for invalidation.</summary>
+    public required long GenerationId { get; init; }
+
+    /// <summary>Root of the trie. Level 0 (cluster-level grants) live directly here.</summary>
+    public PermissionTrieNode Root { get; init; } = new();
+
+    /// <summary>
+    ///     Walk the trie collecting grants that apply to <paramref name="scope"/> for any of the
+    ///     session's <paramref name="ldapGroups"/>. Returns the matched-grant list; the caller
+    ///     OR-s the flag bits to decide whether the requested permission is carried.
+    /// </summary>
+    public IReadOnlyList<MatchedGrant> CollectMatches(NodeScope scope, IEnumerable<string> ldapGroups)
+    {
+        ArgumentNullException.ThrowIfNull(scope);
+        ArgumentNullException.ThrowIfNull(ldapGroups);
+
+        var groups = ldapGroups.ToHashSet(StringComparer.OrdinalIgnoreCase);
+        if (groups.Count == 0) return [];
+
+        var matches = new List<MatchedGrant>();
+
+        // Level 0 — cluster-scoped grants.
+        CollectAtLevel(Root, NodeAclScopeKind.Cluster, groups, matches);
+
+        // Level 1 — namespace.
+        if (scope.NamespaceId is null) return matches;
+        if (!Root.Children.TryGetValue(scope.NamespaceId, out var ns)) return matches;
+        CollectAtLevel(ns, NodeAclScopeKind.Namespace, groups, matches);
+
+        // Two hierarchies diverge below the namespace.
+        if (scope.Kind == NodeHierarchyKind.Equipment)
+            WalkEquipment(ns, scope, groups, matches);
+        else
+            WalkSystemPlatform(ns, scope, groups, matches);
+
+        return matches;
+    }
+
+    private static void WalkEquipment(PermissionTrieNode ns, NodeScope scope, HashSet<string> groups, List<MatchedGrant> matches)
+    {
+        if (scope.UnsAreaId is null) return;
+        if (!ns.Children.TryGetValue(scope.UnsAreaId, out var area)) return;
+        CollectAtLevel(area, NodeAclScopeKind.UnsArea, groups, matches);
+
+        if (scope.UnsLineId is null) return;
+        if (!area.Children.TryGetValue(scope.UnsLineId, out var line)) return;
+        CollectAtLevel(line, NodeAclScopeKind.UnsLine, groups, matches);
+
+        if (scope.EquipmentId is null) return;
+        if (!line.Children.TryGetValue(scope.EquipmentId, out var eq)) return;
+        CollectAtLevel(eq, NodeAclScopeKind.Equipment, groups, matches);
+
+        if (scope.TagId is null) return;
+        if (!eq.Children.TryGetValue(scope.TagId, out var tag)) return;
+        CollectAtLevel(tag, NodeAclScopeKind.Tag, groups, matches);
+    }
+
+    private static void WalkSystemPlatform(PermissionTrieNode ns, NodeScope scope, HashSet<string> groups, List<MatchedGrant> matches)
+    {
+        // FolderSegments are nested under the namespace; each is its own trie level. Reuse the
+        // UnsArea scope kind for the flags — NodeAcl rows for Galaxy tags carry ScopeKind.Tag
+        // for leaf grants and ScopeKind.Namespace for folder-root grants; deeper folder grants
+        // are modeled as Equipment-level rows today since NodeAclScopeKind doesn't enumerate
+        // a dedicated FolderSegment kind. Future-proof TODO tracked in Stream B follow-up.
+        var current = ns;
+        foreach (var segment in scope.FolderSegments)
+        {
+            if (!current.Children.TryGetValue(segment, out var child)) return;
+            CollectAtLevel(child, NodeAclScopeKind.Equipment, groups, matches);
+            current = child;
+        }
+
+        if (scope.TagId is null) return;
+        if (!current.Children.TryGetValue(scope.TagId, out var tag)) return;
+        CollectAtLevel(tag, NodeAclScopeKind.Tag, groups, matches);
+    }
+
+    private static void CollectAtLevel(PermissionTrieNode node, NodeAclScopeKind level, HashSet<string> groups, List<MatchedGrant> matches)
+    {
+        foreach (var grant in node.Grants)
+        {
+            if (groups.Contains(grant.LdapGroup))
+                matches.Add(new MatchedGrant(grant.LdapGroup, level, grant.PermissionFlags));
+        }
+    }
+}
+
+/// <summary>One node in a <see cref="PermissionTrie"/>.</summary>
+public sealed class PermissionTrieNode
+{
+    /// <summary>Grants anchored at this trie level.</summary>
+    public List<TrieGrant> Grants { get; } = [];
+
+    /// <summary>
+    ///     Children keyed by the next level's id — namespace id under cluster; UnsAreaId or
+    ///     folder-segment name under namespace; etc. Comparer is OrdinalIgnoreCase so the walk
+    ///     tolerates case drift between the NodeAcl row and the requested scope.
+    /// </summary>
+    public Dictionary<string, PermissionTrieNode> Children { get; } = new(StringComparer.OrdinalIgnoreCase);
+}
+
+/// <summary>Projection of a <see cref="Configuration.Entities.NodeAcl"/> row into the trie.</summary>
+public sealed record TrieGrant(string LdapGroup, NodePermissions PermissionFlags);

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/PermissionTrieBuilder.cs

@@ -0,0 +1,97 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Builds a <see cref="PermissionTrie"/> from a set of <see cref="NodeAcl"/> rows anchored
+///     in one generation. The trie is keyed on the rows' scope hierarchy — rows with
+///     <see cref="NodeAclScopeKind.Cluster"/> land at the trie root, rows with
+///     <see cref="NodeAclScopeKind.Tag"/> land at a leaf, etc.
+/// </summary>
+/// <remarks>
+///     <para>Intended to be called by <see cref="PermissionTrieCache"/> once per published
+///     generation; the resulting trie is immutable for the life of the cache entry. Idempotent —
+///     two builds from the same rows produce equal tries (grant lists may be in insertion order;
+///     evaluators don't depend on order).</para>
+///
+///     <para>The builder deliberately does not know about the node-row metadata the trie path
+///     will be walked with. The caller assembles <see cref="NodeScope"/> values from the live
+///     config (UnsArea parent of UnsLine, etc.); this class only honors the <c>ScopeId</c>
+///     each row carries.</para>
+/// </remarks>
+public static class PermissionTrieBuilder
+{
+    /// <summary>
+    ///     Build a trie for one cluster/generation from the supplied rows. The caller is
+    ///     responsible for pre-filtering rows to the target generation + cluster.
+    /// </summary>
+    public static PermissionTrie Build(
+        string clusterId,
+        long generationId,
+        IReadOnlyList<NodeAcl> rows,
+        IReadOnlyDictionary<string, NodeAclPath>? scopePaths = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
+        ArgumentNullException.ThrowIfNull(rows);
+
+        var trie = new PermissionTrie { ClusterId = clusterId, GenerationId = generationId };
+
+        foreach (var row in rows)
+        {
+            if (!string.Equals(row.ClusterId, clusterId, StringComparison.OrdinalIgnoreCase)) continue;
+            var grant = new TrieGrant(row.LdapGroup, row.PermissionFlags);
+
+            var node = row.ScopeKind switch
+            {
+                NodeAclScopeKind.Cluster => trie.Root,
+                _ => Descend(trie.Root, row, scopePaths),
+            };
+
+            if (node is not null)
+                node.Grants.Add(grant);
+        }
+
+        return trie;
+    }
+
+    private static PermissionTrieNode? Descend(PermissionTrieNode root, NodeAcl row, IReadOnlyDictionary<string, NodeAclPath>? scopePaths)
+    {
+        if (string.IsNullOrEmpty(row.ScopeId)) return null;
+
+        // For sub-cluster scopes the caller supplies a path lookup so we know the containing
+        // namespace / UnsArea / UnsLine ids. Without a path lookup we fall back to putting the
+        // row directly under the root using its ScopeId — works for deterministic tests, not
+        // for production where the hierarchy must be honored.
+        if (scopePaths is null || !scopePaths.TryGetValue(row.ScopeId, out var path))
+        {
+            return EnsureChild(root, row.ScopeId);
+        }
+
+        var node = root;
+        foreach (var segment in path.Segments)
+            node = EnsureChild(node, segment);
+        return node;
+    }
+
+    private static PermissionTrieNode EnsureChild(PermissionTrieNode parent, string key)
+    {
+        if (!parent.Children.TryGetValue(key, out var child))
+        {
+            child = new PermissionTrieNode();
+            parent.Children[key] = child;
+        }
+        return child;
+    }
+}
+
+/// <summary>
+///     Ordered list of trie-path segments from root to the target node. Supplied to
+///     <see cref="PermissionTrieBuilder.Build"/> so the builder knows where a
+///     <see cref="NodeAclScopeKind.UnsLine"/>-scoped row sits in the hierarchy.
+/// </summary>
+/// <param name="Segments">
+///     Namespace id, then (for Equipment kind) UnsAreaId / UnsLineId / EquipmentId / TagId as
+///     applicable; or (for SystemPlatform kind) NamespaceId / FolderSegment / .../TagId.
+/// </param>
+public sealed record NodeAclPath(IReadOnlyList<string> Segments);

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/PermissionTrieCache.cs

@@ -0,0 +1,88 @@
+using System.Collections.Concurrent;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Process-singleton cache of <see cref="PermissionTrie"/> instances keyed on
+///     <c>(ClusterId, GenerationId)</c>. Hot-path evaluation reads
+///     <see cref="GetTrie(string)"/> without awaiting DB access; the cache is populated
+///     out-of-band on publish + on first reference via
+///     <see cref="Install(PermissionTrie)"/>.
+/// </summary>
+/// <remarks>
+///     Per decision #148 and Phase 6.2 Stream B.4 the cache is generation-sealed: once a
+///     trie is installed for <c>(ClusterId, GenerationId)</c> the entry is immutable. When a
+///     new generation publishes, the caller calls <see cref="Install"/> with the new trie
+///     + the cache atomically updates its "current generation" pointer for that cluster.
+///     Older generations are retained so an in-flight request evaluating the prior generation
+///     still succeeds — GC via <see cref="Prune(string, int)"/>.
+/// </remarks>
+public sealed class PermissionTrieCache
+{
+    private readonly ConcurrentDictionary<string, ClusterEntry> _byCluster =
+        new(StringComparer.OrdinalIgnoreCase);
+
+    /// <summary>Install a trie for a cluster + make it the current generation.</summary>
+    public void Install(PermissionTrie trie)
+    {
+        ArgumentNullException.ThrowIfNull(trie);
+        _byCluster.AddOrUpdate(trie.ClusterId,
+            _ => ClusterEntry.FromSingle(trie),
+            (_, existing) => existing.WithAdditional(trie));
+    }
+
+    /// <summary>Get the current-generation trie for a cluster; null when nothing installed.</summary>
+    public PermissionTrie? GetTrie(string clusterId)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(clusterId);
+        return _byCluster.TryGetValue(clusterId, out var entry) ? entry.Current : null;
+    }
+
+    /// <summary>Get a specific (cluster, generation) trie; null if that pair isn't cached.</summary>
+    public PermissionTrie? GetTrie(string clusterId, long generationId)
+    {
+        if (!_byCluster.TryGetValue(clusterId, out var entry)) return null;
+        return entry.Tries.TryGetValue(generationId, out var trie) ? trie : null;
+    }
+
+    /// <summary>The generation id the <see cref="GetTrie(string)"/> shortcut currently serves for a cluster.</summary>
+    public long? CurrentGenerationId(string clusterId)
+        => _byCluster.TryGetValue(clusterId, out var entry) ? entry.Current.GenerationId : null;
+
+    /// <summary>Drop every cached trie for one cluster.</summary>
+    public void Invalidate(string clusterId) => _byCluster.TryRemove(clusterId, out _);
+
+    /// <summary>
+    ///     Retain only the most-recent <paramref name="keepLatest"/> generations for a cluster.
+    ///     No-op when there's nothing to drop.
+    /// </summary>
+    public void Prune(string clusterId, int keepLatest = 3)
+    {
+        if (keepLatest < 1) throw new ArgumentOutOfRangeException(nameof(keepLatest), keepLatest, "keepLatest must be >= 1");
+        if (!_byCluster.TryGetValue(clusterId, out var entry)) return;
+
+        if (entry.Tries.Count <= keepLatest) return;
+        var keep = entry.Tries
+            .OrderByDescending(kvp => kvp.Key)
+            .Take(keepLatest)
+            .ToDictionary(kvp => kvp.Key, kvp => kvp.Value);
+        _byCluster[clusterId] = new ClusterEntry(entry.Current, keep);
+    }
+
+    /// <summary>Diagnostics counter: number of cached (cluster, generation) tries.</summary>
+    public int CachedTrieCount => _byCluster.Values.Sum(e => e.Tries.Count);
+
+    private sealed record ClusterEntry(PermissionTrie Current, IReadOnlyDictionary<long, PermissionTrie> Tries)
+    {
+        public static ClusterEntry FromSingle(PermissionTrie trie) =>
+            new(trie, new Dictionary<long, PermissionTrie> { [trie.GenerationId] = trie });
+
+        public ClusterEntry WithAdditional(PermissionTrie trie)
+        {
+            var next = new Dictionary<long, PermissionTrie>(Tries) { [trie.GenerationId] = trie };
+            // The highest generation wins as "current" — handles out-of-order installs.
+            var current = trie.GenerationId >= Current.GenerationId ? trie : Current;
+            return new ClusterEntry(current, next);
+        }
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/TriePermissionEvaluator.cs

@@ -0,0 +1,70 @@
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Default <see cref="IPermissionEvaluator"/> implementation. Resolves the
+///     <see cref="PermissionTrie"/> for the session's cluster (via
+///     <see cref="PermissionTrieCache"/>), walks it collecting matched grants, OR-s the
+///     permission flags, and maps against the operation-specific required permission.
+/// </summary>
+public sealed class TriePermissionEvaluator : IPermissionEvaluator
+{
+    private readonly PermissionTrieCache _cache;
+    private readonly TimeProvider _timeProvider;
+
+    public TriePermissionEvaluator(PermissionTrieCache cache, TimeProvider? timeProvider = null)
+    {
+        ArgumentNullException.ThrowIfNull(cache);
+        _cache = cache;
+        _timeProvider = timeProvider ?? TimeProvider.System;
+    }
+
+    public AuthorizationDecision Authorize(UserAuthorizationState session, OpcUaOperation operation, NodeScope scope)
+    {
+        ArgumentNullException.ThrowIfNull(session);
+        ArgumentNullException.ThrowIfNull(scope);
+
+        // Decision #152 — beyond the staleness ceiling every call fails closed regardless of
+        // cache warmth elsewhere in the process.
+        if (session.IsStale(_timeProvider.GetUtcNow().UtcDateTime))
+            return AuthorizationDecision.NotGranted();
+
+        if (!string.Equals(session.ClusterId, scope.ClusterId, StringComparison.OrdinalIgnoreCase))
+            return AuthorizationDecision.NotGranted();
+
+        var trie = _cache.GetTrie(scope.ClusterId);
+        if (trie is null) return AuthorizationDecision.NotGranted();
+
+        var matches = trie.CollectMatches(scope, session.LdapGroups);
+        if (matches.Count == 0) return AuthorizationDecision.NotGranted();
+
+        var required = MapOperationToPermission(operation);
+        var granted = NodePermissions.None;
+        foreach (var m in matches) granted |= m.PermissionFlags;
+
+        return (granted & required) == required
+            ? AuthorizationDecision.Allowed(matches)
+            : AuthorizationDecision.NotGranted();
+    }
+
+    /// <summary>Maps each <see cref="OpcUaOperation"/> to the <see cref="NodePermissions"/> bit required to grant it.</summary>
+    public static NodePermissions MapOperationToPermission(OpcUaOperation op) => op switch
+    {
+        OpcUaOperation.Browse               => NodePermissions.Browse,
+        OpcUaOperation.Read                 => NodePermissions.Read,
+        OpcUaOperation.WriteOperate         => NodePermissions.WriteOperate,
+        OpcUaOperation.WriteTune            => NodePermissions.WriteTune,
+        OpcUaOperation.WriteConfigure       => NodePermissions.WriteConfigure,
+        OpcUaOperation.HistoryRead          => NodePermissions.HistoryRead,
+        OpcUaOperation.HistoryUpdate        => NodePermissions.HistoryRead, // HistoryUpdate bit not yet in NodePermissions; TODO Stream C follow-up
+        OpcUaOperation.CreateMonitoredItems => NodePermissions.Subscribe,
+        OpcUaOperation.TransferSubscriptions=> NodePermissions.Subscribe,
+        OpcUaOperation.Call                 => NodePermissions.MethodCall,
+        OpcUaOperation.AlarmAcknowledge     => NodePermissions.AlarmAcknowledge,
+        OpcUaOperation.AlarmConfirm         => NodePermissions.AlarmConfirm,
+        OpcUaOperation.AlarmShelve          => NodePermissions.AlarmShelve,
+        _ => throw new ArgumentOutOfRangeException(nameof(op), op, $"No permission mapping defined for operation {op}."),
+    };
+}

src/ZB.MOM.WW.OtOpcUa.Core/Authorization/UserAuthorizationState.cs

@@ -0,0 +1,69 @@
+namespace ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+/// <summary>
+///     Per-session authorization state cached on the OPC UA session object + keyed on the
+///     session id. Captures the LDAP group memberships resolved at sign-in, the generation
+///     the membership was resolved against, and the bounded freshness window.
+/// </summary>
+/// <remarks>
+///     Per decision #151 the membership is bounded by <see cref="MembershipFreshnessInterval"/>
+///     (default 15 min). After that, the next hot-path authz call re-resolves LDAP group
+///     memberships; failure to re-resolve (LDAP unreachable) flips the session to fail-closed
+///     until a refresh succeeds.
+///
+///     Per decision #152 <see cref="AuthCacheMaxStaleness"/> (default 5 min) is separate from
+///     Phase 6.1's availability-oriented 24h cache — beyond this window the evaluator returns
+///     <see cref="AuthorizationVerdict.NotGranted"/> regardless of config-cache warmth.
+/// </remarks>
+public sealed record UserAuthorizationState
+{
+    /// <summary>Opaque session id (reuse OPC UA session handle when possible).</summary>
+    public required string SessionId { get; init; }
+
+    /// <summary>Cluster the session is scoped to — every request targets nodes in this cluster.</summary>
+    public required string ClusterId { get; init; }
+
+    /// <summary>
+    ///     LDAP groups the user is a member of as resolved at sign-in / last membership refresh.
+    ///     Case comparison is handled downstream by the evaluator (OrdinalIgnoreCase).
+    /// </summary>
+    public required IReadOnlyList<string> LdapGroups { get; init; }
+
+    /// <summary>Timestamp when <see cref="LdapGroups"/> was last resolved from the directory.</summary>
+    public required DateTime MembershipResolvedUtc { get; init; }
+
+    /// <summary>
+    ///     Trie generation the session is currently bound to. When
+    ///     <see cref="PermissionTrieCache"/> moves to a new generation, the session's
+    ///     <c>(AuthGenerationId, MembershipVersion)</c> stamp no longer matches its
+    ///     MonitoredItems and they re-evaluate on next publish (decision #153).
+    /// </summary>
+    public required long AuthGenerationId { get; init; }
+
+    /// <summary>
+    ///     Monotonic counter incremented every time membership is re-resolved. Combined with
+    ///     <see cref="AuthGenerationId"/> into the subscription stamp per decision #153.
+    /// </summary>
+    public required long MembershipVersion { get; init; }
+
+    /// <summary>Bounded membership freshness window; past this the next authz call refreshes.</summary>
+    public TimeSpan MembershipFreshnessInterval { get; init; } = TimeSpan.FromMinutes(15);
+
+    /// <summary>Hard staleness ceiling — beyond this, the evaluator fails closed.</summary>
+    public TimeSpan AuthCacheMaxStaleness { get; init; } = TimeSpan.FromMinutes(5);
+
+    /// <summary>
+    ///     True when <paramref name="utcNow"/> - <see cref="MembershipResolvedUtc"/> exceeds
+    ///     <see cref="AuthCacheMaxStaleness"/>. The evaluator short-circuits to NotGranted
+    ///     whenever this is true.
+    /// </summary>
+    public bool IsStale(DateTime utcNow) => utcNow - MembershipResolvedUtc > AuthCacheMaxStaleness;
+
+    /// <summary>
+    ///     True when membership is past its freshness interval but still within the staleness
+    ///     ceiling — a signal to the caller to kick off an async refresh, while the current
+    ///     call still evaluates against the cached memberships.
+    /// </summary>
+    public bool NeedsRefresh(DateTime utcNow) =>
+        !IsStale(utcNow) && utcNow - MembershipResolvedUtc > MembershipFreshnessInterval;
+}

src/ZB.MOM.WW.OtOpcUa.Server/Security/AuthorizationGate.cs

@@ -0,0 +1,86 @@
+using Opc.Ua;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Security;
+
+/// <summary>
+///     Bridges the OPC UA stack's <see cref="ISystemContext.UserIdentity"/> to the
+///     <see cref="IPermissionEvaluator"/> evaluator. Resolves the session's
+///     <see cref="UserAuthorizationState"/> from whatever the identity claims + the stack's
+///     session handle, then delegates to the evaluator and returns a single bool the
+///     dispatch paths can use to short-circuit with <c>BadUserAccessDenied</c>.
+/// </summary>
+/// <remarks>
+///     <para>This class is deliberately the single integration seam between the Server
+///     project and the <c>Core.Authorization</c> evaluator. DriverNodeManager holds one
+///     reference and calls <see cref="IsAllowed"/> on every Read / Write / HistoryRead /
+///     Browse / Call / CreateMonitoredItems / etc. The evaluator itself stays pure — it
+///     doesn't know about the OPC UA stack types.</para>
+///
+///     <para>Fail-open-during-transition: when the evaluator is configured with
+///     <c>StrictMode = false</c>, missing cluster tries OR sessions without resolved
+///     LDAP groups get <c>true</c> so existing deployments keep working while ACLs are
+///     populated. Flip to strict via <c>Authorization:StrictMode = true</c> in production.</para>
+/// </remarks>
+public sealed class AuthorizationGate
+{
+    private readonly IPermissionEvaluator _evaluator;
+    private readonly bool _strictMode;
+    private readonly TimeProvider _timeProvider;
+
+    public AuthorizationGate(IPermissionEvaluator evaluator, bool strictMode = false, TimeProvider? timeProvider = null)
+    {
+        _evaluator = evaluator ?? throw new ArgumentNullException(nameof(evaluator));
+        _strictMode = strictMode;
+        _timeProvider = timeProvider ?? TimeProvider.System;
+    }
+
+    /// <summary>True when strict authorization is enabled — no-grant = denied.</summary>
+    public bool StrictMode => _strictMode;
+
+    /// <summary>
+    ///     Authorize an OPC UA operation against the session identity + scope. Returns true to
+    ///     allow the dispatch to continue; false to surface <c>BadUserAccessDenied</c>.
+    /// </summary>
+    public bool IsAllowed(IUserIdentity? identity, OpcUaOperation operation, NodeScope scope)
+    {
+        // Anonymous / unknown identity — strict mode denies, lax mode allows so the fallback
+        // auth layers (WriteAuthzPolicy) still see the call.
+        if (identity is null) return !_strictMode;
+
+        var session = BuildSessionState(identity, scope.ClusterId);
+        if (session is null)
+        {
+            // Identity doesn't carry LDAP groups. In lax mode let the dispatch proceed so
+            // older deployments keep working; strict mode denies.
+            return !_strictMode;
+        }
+
+        var decision = _evaluator.Authorize(session, operation, scope);
+        if (decision.IsAllowed) return true;
+
+        return !_strictMode;
+    }
+
+    /// <summary>
+    ///     Materialize a <see cref="UserAuthorizationState"/> from the session identity.
+    ///     Returns null when the identity doesn't carry LDAP group metadata.
+    /// </summary>
+    public UserAuthorizationState? BuildSessionState(IUserIdentity identity, string clusterId)
+    {
+        if (identity is not ILdapGroupsBearer bearer || bearer.LdapGroups.Count == 0)
+            return null;
+
+        var sessionId = identity.DisplayName ?? Guid.NewGuid().ToString("N");
+        return new UserAuthorizationState
+        {
+            SessionId = sessionId,
+            ClusterId = clusterId,
+            LdapGroups = bearer.LdapGroups,
+            MembershipResolvedUtc = _timeProvider.GetUtcNow().UtcDateTime,
+            AuthGenerationId = 0,
+            MembershipVersion = 0,
+        };
+    }
+}

src/ZB.MOM.WW.OtOpcUa.Server/Security/ILdapGroupsBearer.cs

@@ -0,0 +1,20 @@
+namespace ZB.MOM.WW.OtOpcUa.Server.Security;
+
+/// <summary>
+///     Minimal interface an <see cref="Opc.Ua.IUserIdentity"/> exposes so the Phase 6.2
+///     authorization evaluator can read the session's resolved LDAP group DNs without a
+///     hard dependency on any specific identity subtype. Implemented by OtOpcUaServer's
+///     role-based identity; tests stub it to drive the evaluator under different group
+///     memberships.
+/// </summary>
+/// <remarks>
+///     Control/data-plane separation (decision #150): Admin UI role routing consumes
+///     <see cref="IRoleBearer.Roles"/> via <c>LdapGroupRoleMapping</c>; the OPC UA data-path
+///     evaluator consumes <see cref="LdapGroups"/> directly against <c>NodeAcl</c>. The two
+///     are sourced from the same directory query at sign-in but never cross.
+/// </remarks>
+public interface ILdapGroupsBearer
+{
+    /// <summary>Fully-qualified LDAP group DNs the user is a member of.</summary>
+    IReadOnlyList<string> LdapGroups { get; }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/Authorization/PermissionTrieCacheTests.cs

@@ -0,0 +1,104 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Authorization;
+
+[Trait("Category", "Unit")]
+public sealed class PermissionTrieCacheTests
+{
+    private static PermissionTrie Trie(string cluster, long generation) => new()
+    {
+        ClusterId = cluster,
+        GenerationId = generation,
+    };
+
+    [Fact]
+    public void GetTrie_Empty_ReturnsNull()
+    {
+        new PermissionTrieCache().GetTrie("c1").ShouldBeNull();
+    }
+
+    [Fact]
+    public void Install_ThenGet_RoundTrips()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 5));
+
+        cache.GetTrie("c1")!.GenerationId.ShouldBe(5);
+        cache.CurrentGenerationId("c1").ShouldBe(5);
+    }
+
+    [Fact]
+    public void NewGeneration_BecomesCurrent()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 1));
+        cache.Install(Trie("c1", 2));
+
+        cache.CurrentGenerationId("c1").ShouldBe(2);
+        cache.GetTrie("c1", 1).ShouldNotBeNull("prior generation retained for in-flight requests");
+        cache.GetTrie("c1", 2).ShouldNotBeNull();
+    }
+
+    [Fact]
+    public void OutOfOrder_Install_DoesNotDowngrade_Current()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 3));
+        cache.Install(Trie("c1", 1)); // late-arriving older generation
+
+        cache.CurrentGenerationId("c1").ShouldBe(3, "older generation must not become current");
+        cache.GetTrie("c1", 1).ShouldNotBeNull("but older is still retrievable by explicit lookup");
+    }
+
+    [Fact]
+    public void Invalidate_DropsCluster()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 1));
+        cache.Install(Trie("c2", 1));
+
+        cache.Invalidate("c1");
+
+        cache.GetTrie("c1").ShouldBeNull();
+        cache.GetTrie("c2").ShouldNotBeNull("sibling cluster unaffected");
+    }
+
+    [Fact]
+    public void Prune_RetainsMostRecent()
+    {
+        var cache = new PermissionTrieCache();
+        for (var g = 1L; g <= 5; g++) cache.Install(Trie("c1", g));
+
+        cache.Prune("c1", keepLatest: 2);
+
+        cache.GetTrie("c1", 5).ShouldNotBeNull();
+        cache.GetTrie("c1", 4).ShouldNotBeNull();
+        cache.GetTrie("c1", 3).ShouldBeNull();
+        cache.GetTrie("c1", 1).ShouldBeNull();
+    }
+
+    [Fact]
+    public void Prune_LessThanKeep_IsNoOp()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 1));
+        cache.Install(Trie("c1", 2));
+
+        cache.Prune("c1", keepLatest: 10);
+
+        cache.CachedTrieCount.ShouldBe(2);
+    }
+
+    [Fact]
+    public void ClusterIsolation()
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(Trie("c1", 1));
+        cache.Install(Trie("c2", 9));
+
+        cache.CurrentGenerationId("c1").ShouldBe(1);
+        cache.CurrentGenerationId("c2").ShouldBe(9);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/Authorization/PermissionTrieTests.cs

@@ -0,0 +1,157 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Authorization;
+
+[Trait("Category", "Unit")]
+public sealed class PermissionTrieTests
+{
+    private static NodeAcl Row(string group, NodeAclScopeKind scope, string? scopeId, NodePermissions flags, string clusterId = "c1") =>
+        new()
+        {
+            NodeAclRowId = Guid.NewGuid(),
+            NodeAclId = $"acl-{Guid.NewGuid():N}",
+            GenerationId = 1,
+            ClusterId = clusterId,
+            LdapGroup = group,
+            ScopeKind = scope,
+            ScopeId = scopeId,
+            PermissionFlags = flags,
+        };
+
+    private static NodeScope EquipmentTag(string cluster, string ns, string area, string line, string equip, string tag) =>
+        new()
+        {
+            ClusterId = cluster,
+            NamespaceId = ns,
+            UnsAreaId = area,
+            UnsLineId = line,
+            EquipmentId = equip,
+            TagId = tag,
+            Kind = NodeHierarchyKind.Equipment,
+        };
+
+    private static NodeScope GalaxyTag(string cluster, string ns, string[] folders, string tag) =>
+        new()
+        {
+            ClusterId = cluster,
+            NamespaceId = ns,
+            FolderSegments = folders,
+            TagId = tag,
+            Kind = NodeHierarchyKind.SystemPlatform,
+        };
+
+    [Fact]
+    public void ClusterLevelGrant_Cascades_ToEveryTag()
+    {
+        var rows = new[] { Row("cn=ops", NodeAclScopeKind.Cluster, scopeId: null, NodePermissions.Read) };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows);
+
+        var matches = trie.CollectMatches(
+            EquipmentTag("c1", "ns", "area1", "line1", "eq1", "tag1"),
+            ["cn=ops"]);
+
+        matches.Count.ShouldBe(1);
+        matches[0].PermissionFlags.ShouldBe(NodePermissions.Read);
+        matches[0].Scope.ShouldBe(NodeAclScopeKind.Cluster);
+    }
+
+    [Fact]
+    public void EquipmentScope_DoesNotLeak_ToSibling()
+    {
+        var paths = new Dictionary<string, NodeAclPath>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["eq-A"] = new(new[] { "ns", "area1", "line1", "eq-A" }),
+        };
+        var rows = new[] { Row("cn=ops", NodeAclScopeKind.Equipment, "eq-A", NodePermissions.Read) };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows, paths);
+
+        var matchA = trie.CollectMatches(EquipmentTag("c1", "ns", "area1", "line1", "eq-A", "tag1"), ["cn=ops"]);
+        var matchB = trie.CollectMatches(EquipmentTag("c1", "ns", "area1", "line1", "eq-B", "tag1"), ["cn=ops"]);
+
+        matchA.Count.ShouldBe(1);
+        matchB.ShouldBeEmpty("grant at eq-A must not apply to sibling eq-B");
+    }
+
+    [Fact]
+    public void MultiGroup_Union_OrsPermissionFlags()
+    {
+        var rows = new[]
+        {
+            Row("cn=readers", NodeAclScopeKind.Cluster, null, NodePermissions.Read),
+            Row("cn=writers", NodeAclScopeKind.Cluster, null, NodePermissions.WriteOperate),
+        };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows);
+
+        var matches = trie.CollectMatches(
+            EquipmentTag("c1", "ns", "area1", "line1", "eq1", "tag1"),
+            ["cn=readers", "cn=writers"]);
+
+        matches.Count.ShouldBe(2);
+        var combined = matches.Aggregate(NodePermissions.None, (acc, m) => acc | m.PermissionFlags);
+        combined.ShouldBe(NodePermissions.Read | NodePermissions.WriteOperate);
+    }
+
+    [Fact]
+    public void NoMatchingGroup_ReturnsEmpty()
+    {
+        var rows = new[] { Row("cn=different", NodeAclScopeKind.Cluster, null, NodePermissions.Read) };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows);
+
+        var matches = trie.CollectMatches(
+            EquipmentTag("c1", "ns", "area1", "line1", "eq1", "tag1"),
+            ["cn=ops"]);
+
+        matches.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void Galaxy_FolderSegment_Grant_DoesNotLeak_To_Sibling_Folder()
+    {
+        var paths = new Dictionary<string, NodeAclPath>(StringComparer.OrdinalIgnoreCase)
+        {
+            ["folder-A"] = new(new[] { "ns-gal", "folder-A" }),
+        };
+        var rows = new[] { Row("cn=ops", NodeAclScopeKind.Equipment, "folder-A", NodePermissions.Read) };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows, paths);
+
+        var matchA = trie.CollectMatches(GalaxyTag("c1", "ns-gal", ["folder-A"], "tag1"), ["cn=ops"]);
+        var matchB = trie.CollectMatches(GalaxyTag("c1", "ns-gal", ["folder-B"], "tag1"), ["cn=ops"]);
+
+        matchA.Count.ShouldBe(1);
+        matchB.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void CrossCluster_Grant_DoesNotLeak()
+    {
+        var rows = new[] { Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read, clusterId: "c-other") };
+        var trie = PermissionTrieBuilder.Build("c1", 1, rows);
+
+        var matches = trie.CollectMatches(
+            EquipmentTag("c1", "ns", "area1", "line1", "eq1", "tag1"),
+            ["cn=ops"]);
+
+        matches.ShouldBeEmpty("rows for cluster c-other must not land in c1's trie");
+    }
+
+    [Fact]
+    public void Build_IsIdempotent()
+    {
+        var rows = new[]
+        {
+            Row("cn=a", NodeAclScopeKind.Cluster, null, NodePermissions.Read),
+            Row("cn=b", NodeAclScopeKind.Cluster, null, NodePermissions.WriteOperate),
+        };
+
+        var trie1 = PermissionTrieBuilder.Build("c1", 1, rows);
+        var trie2 = PermissionTrieBuilder.Build("c1", 1, rows);
+
+        trie1.Root.Grants.Count.ShouldBe(trie2.Root.Grants.Count);
+        trie1.ClusterId.ShouldBe(trie2.ClusterId);
+        trie1.GenerationId.ShouldBe(trie2.GenerationId);
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/Authorization/TriePermissionEvaluatorTests.cs

@@ -0,0 +1,154 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Authorization;
+
+[Trait("Category", "Unit")]
+public sealed class TriePermissionEvaluatorTests
+{
+    private static readonly DateTime Now = new(2026, 4, 19, 12, 0, 0, DateTimeKind.Utc);
+    private readonly FakeTimeProvider _time = new();
+
+    private sealed class FakeTimeProvider : TimeProvider
+    {
+        public DateTime Utc { get; set; } = Now;
+        public override DateTimeOffset GetUtcNow() => new(Utc, TimeSpan.Zero);
+    }
+
+    private static NodeAcl Row(string group, NodeAclScopeKind scope, string? scopeId, NodePermissions flags) =>
+        new()
+        {
+            NodeAclRowId = Guid.NewGuid(),
+            NodeAclId = $"acl-{Guid.NewGuid():N}",
+            GenerationId = 1,
+            ClusterId = "c1",
+            LdapGroup = group,
+            ScopeKind = scope,
+            ScopeId = scopeId,
+            PermissionFlags = flags,
+        };
+
+    private static UserAuthorizationState Session(string[] groups, DateTime? resolvedUtc = null, string clusterId = "c1") =>
+        new()
+        {
+            SessionId = "sess",
+            ClusterId = clusterId,
+            LdapGroups = groups,
+            MembershipResolvedUtc = resolvedUtc ?? Now,
+            AuthGenerationId = 1,
+            MembershipVersion = 1,
+        };
+
+    private static NodeScope Scope(string cluster = "c1") =>
+        new()
+        {
+            ClusterId = cluster,
+            NamespaceId = "ns",
+            UnsAreaId = "area",
+            UnsLineId = "line",
+            EquipmentId = "eq",
+            TagId = "tag",
+            Kind = NodeHierarchyKind.Equipment,
+        };
+
+    private TriePermissionEvaluator MakeEvaluator(NodeAcl[] rows)
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(PermissionTrieBuilder.Build("c1", 1, rows));
+        return new TriePermissionEvaluator(cache, _time);
+    }
+
+    [Fact]
+    public void Allow_When_RequiredFlag_Matched()
+    {
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+
+        var decision = evaluator.Authorize(Session(["cn=ops"]), OpcUaOperation.Read, Scope());
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.Allow);
+        decision.Provenance.Count.ShouldBe(1);
+    }
+
+    [Fact]
+    public void NotGranted_When_NoMatchingGroup()
+    {
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+
+        var decision = evaluator.Authorize(Session(["cn=unrelated"]), OpcUaOperation.Read, Scope());
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.NotGranted);
+        decision.Provenance.ShouldBeEmpty();
+    }
+
+    [Fact]
+    public void NotGranted_When_FlagsInsufficient()
+    {
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+
+        var decision = evaluator.Authorize(Session(["cn=ops"]), OpcUaOperation.WriteOperate, Scope());
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.NotGranted);
+    }
+
+    [Fact]
+    public void HistoryRead_Requires_Its_Own_Bit()
+    {
+        // User has Read but not HistoryRead
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+
+        var liveRead = evaluator.Authorize(Session(["cn=ops"]), OpcUaOperation.Read, Scope());
+        var historyRead = evaluator.Authorize(Session(["cn=ops"]), OpcUaOperation.HistoryRead, Scope());
+
+        liveRead.IsAllowed.ShouldBeTrue();
+        historyRead.IsAllowed.ShouldBeFalse("HistoryRead uses its own NodePermissions flag, not Read");
+    }
+
+    [Fact]
+    public void CrossCluster_Session_Denied()
+    {
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+        var otherSession = Session(["cn=ops"], clusterId: "c-other");
+
+        var decision = evaluator.Authorize(otherSession, OpcUaOperation.Read, Scope(cluster: "c1"));
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.NotGranted);
+    }
+
+    [Fact]
+    public void StaleSession_FailsClosed()
+    {
+        var evaluator = MakeEvaluator([Row("cn=ops", NodeAclScopeKind.Cluster, null, NodePermissions.Read)]);
+        var session = Session(["cn=ops"], resolvedUtc: Now);
+        _time.Utc = Now.AddMinutes(10); // well past the 5-min AuthCacheMaxStaleness default
+
+        var decision = evaluator.Authorize(session, OpcUaOperation.Read, Scope());
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.NotGranted);
+    }
+
+    [Fact]
+    public void NoCachedTrie_ForCluster_Denied()
+    {
+        var cache = new PermissionTrieCache();  // empty cache
+        var evaluator = new TriePermissionEvaluator(cache, _time);
+
+        var decision = evaluator.Authorize(Session(["cn=ops"]), OpcUaOperation.Read, Scope());
+
+        decision.Verdict.ShouldBe(AuthorizationVerdict.NotGranted);
+    }
+
+    [Fact]
+    public void OperationToPermission_Mapping_IsTotal()
+    {
+        foreach (var op in Enum.GetValues<OpcUaOperation>())
+        {
+            // Must not throw — every OpcUaOperation needs a mapping or the compliance-check
+            // "every operation wired" fails.
+            TriePermissionEvaluator.MapOperationToPermission(op);
+        }
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Core.Tests/Authorization/UserAuthorizationStateTests.cs

@@ -0,0 +1,60 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+
+namespace ZB.MOM.WW.OtOpcUa.Core.Tests.Authorization;
+
+[Trait("Category", "Unit")]
+public sealed class UserAuthorizationStateTests
+{
+    private static readonly DateTime Now = new(2026, 4, 19, 12, 0, 0, DateTimeKind.Utc);
+
+    private static UserAuthorizationState Fresh(DateTime resolved) => new()
+    {
+        SessionId = "s",
+        ClusterId = "c1",
+        LdapGroups = ["cn=ops"],
+        MembershipResolvedUtc = resolved,
+        AuthGenerationId = 1,
+        MembershipVersion = 1,
+    };
+
+    [Fact]
+    public void FreshlyResolved_Is_NotStale_NorNeedsRefresh()
+    {
+        var session = Fresh(Now);
+
+        session.IsStale(Now.AddMinutes(1)).ShouldBeFalse();
+        session.NeedsRefresh(Now.AddMinutes(1)).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void NeedsRefresh_FiresAfter_FreshnessInterval()
+    {
+        var session = Fresh(Now);
+
+        session.NeedsRefresh(Now.AddMinutes(16)).ShouldBeFalse("past freshness but also past the 5-min staleness ceiling — should be Stale, not NeedsRefresh");
+    }
+
+    [Fact]
+    public void NeedsRefresh_TrueBetween_Freshness_And_Staleness_Windows()
+    {
+        // Custom: freshness=2 min, staleness=10 min → between 2 and 10 min NeedsRefresh fires.
+        var session = Fresh(Now) with
+        {
+            MembershipFreshnessInterval = TimeSpan.FromMinutes(2),
+            AuthCacheMaxStaleness = TimeSpan.FromMinutes(10),
+        };
+
+        session.NeedsRefresh(Now.AddMinutes(5)).ShouldBeTrue();
+        session.IsStale(Now.AddMinutes(5)).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void IsStale_TrueAfter_StalenessWindow()
+    {
+        var session = Fresh(Now);
+
+        session.IsStale(Now.AddMinutes(6)).ShouldBeTrue("default AuthCacheMaxStaleness is 5 min");
+    }
+}

tests/ZB.MOM.WW.OtOpcUa.Server.Tests/AuthorizationGateTests.cs

@@ -0,0 +1,136 @@
+using Opc.Ua;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Configuration.Entities;
+using ZB.MOM.WW.OtOpcUa.Configuration.Enums;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Authorization;
+using ZB.MOM.WW.OtOpcUa.Server.Security;
+
+namespace ZB.MOM.WW.OtOpcUa.Server.Tests;
+
+[Trait("Category", "Unit")]
+public sealed class AuthorizationGateTests
+{
+    private static NodeScope Scope(string cluster = "c1", string? tag = "tag1") => new()
+    {
+        ClusterId = cluster,
+        NamespaceId = "ns",
+        UnsAreaId = "area",
+        UnsLineId = "line",
+        EquipmentId = "eq",
+        TagId = tag,
+        Kind = NodeHierarchyKind.Equipment,
+    };
+
+    private static NodeAcl Row(string group, NodePermissions flags) => new()
+    {
+        NodeAclRowId = Guid.NewGuid(),
+        NodeAclId = Guid.NewGuid().ToString(),
+        GenerationId = 1,
+        ClusterId = "c1",
+        LdapGroup = group,
+        ScopeKind = NodeAclScopeKind.Cluster,
+        ScopeId = null,
+        PermissionFlags = flags,
+    };
+
+    private static AuthorizationGate MakeGate(bool strict, NodeAcl[] rows)
+    {
+        var cache = new PermissionTrieCache();
+        cache.Install(PermissionTrieBuilder.Build("c1", 1, rows));
+        var evaluator = new TriePermissionEvaluator(cache);
+        return new AuthorizationGate(evaluator, strictMode: strict);
+    }
+
+    private sealed class FakeIdentity : UserIdentity, ILdapGroupsBearer
+    {
+        public FakeIdentity(string name, IReadOnlyList<string> groups)
+        {
+            DisplayName = name;
+            LdapGroups = groups;
+        }
+        public new string DisplayName { get; }
+        public IReadOnlyList<string> LdapGroups { get; }
+    }
+
+    [Fact]
+    public void NullIdentity_StrictMode_Denies()
+    {
+        var gate = MakeGate(strict: true, rows: []);
+        gate.IsAllowed(null, OpcUaOperation.Read, Scope()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void NullIdentity_LaxMode_Allows()
+    {
+        var gate = MakeGate(strict: false, rows: []);
+        gate.IsAllowed(null, OpcUaOperation.Read, Scope()).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void IdentityWithoutLdapGroups_StrictMode_Denies()
+    {
+        var gate = MakeGate(strict: true, rows: []);
+        var identity = new UserIdentity(); // anonymous, no LDAP groups
+
+        gate.IsAllowed(identity, OpcUaOperation.Read, Scope()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void IdentityWithoutLdapGroups_LaxMode_Allows()
+    {
+        var gate = MakeGate(strict: false, rows: []);
+        var identity = new UserIdentity();
+
+        gate.IsAllowed(identity, OpcUaOperation.Read, Scope()).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void LdapGroupWithGrant_Allows()
+    {
+        var gate = MakeGate(strict: true, rows: [Row("cn=ops", NodePermissions.Read)]);
+        var identity = new FakeIdentity("ops-user", ["cn=ops"]);
+
+        gate.IsAllowed(identity, OpcUaOperation.Read, Scope()).ShouldBeTrue();
+    }
+
+    [Fact]
+    public void LdapGroupWithoutGrant_StrictMode_Denies()
+    {
+        var gate = MakeGate(strict: true, rows: [Row("cn=ops", NodePermissions.Read)]);
+        var identity = new FakeIdentity("other-user", ["cn=other"]);
+
+        gate.IsAllowed(identity, OpcUaOperation.Read, Scope()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void WrongOperation_Denied()
+    {
+        var gate = MakeGate(strict: true, rows: [Row("cn=ops", NodePermissions.Read)]);
+        var identity = new FakeIdentity("ops-user", ["cn=ops"]);
+
+        gate.IsAllowed(identity, OpcUaOperation.WriteOperate, Scope()).ShouldBeFalse();
+    }
+
+    [Fact]
+    public void BuildSessionState_IncludesLdapGroups()
+    {
+        var gate = MakeGate(strict: true, rows: []);
+        var identity = new FakeIdentity("u", ["cn=a", "cn=b"]);
+
+        var state = gate.BuildSessionState(identity, "c1");
+
+        state.ShouldNotBeNull();
+        state!.LdapGroups.Count.ShouldBe(2);
+        state.ClusterId.ShouldBe("c1");
+    }
+
+    [Fact]
+    public void BuildSessionState_ReturnsNull_ForIdentityWithoutLdapGroups()
+    {
+        var gate = MakeGate(strict: true, rows: []);
+
+        gate.BuildSessionState(new UserIdentity(), "c1").ShouldBeNull();
+    }
+}