Classify SGU accounts into AD role groups

src/SGU.AuthBroker/Services/ActiveDirectorySynchronizer.cs

@@ -109,6 +109,12 @@ public sealed class ActiveDirectorySynchronizer(
                 user.CommitChanges();
             }
 
+            // Role membership is part of account provisioning, not optional
+            // enrichment. Do it before changing the password so a missing or
+            // inaccessible authorization group cannot leave a newly usable
+            // account without its required classification.
+            EnsureRoleGroupMembership(user, identity);
+
             // The exact institutional password received by the broker is passed to AD.
             // It is not derived, transformed, written to disk, or included in logs.
             user.Invoke("SetPassword", [password]);
@@ -195,6 +201,33 @@ public sealed class ActiveDirectorySynchronizer(
         }
     }
 
+    private void EnsureRoleGroupMembership(DirectoryEntry user, UserIdentity identity)
+    {
+        user.RefreshCache(["distinguishedName"]);
+        string? userDn = Convert.ToString(user.Properties["distinguishedName"].Value);
+        if (string.IsNullOrWhiteSpace(userDn))
+        {
+            throw new InvalidOperationException($"Active Directory did not return a distinguished name for {identity.UserName}.");
+        }
+
+        string groupDn = options.GetGroupDn(identity.Role);
+        using DirectoryEntry group = Bind(groupDn);
+        _ = group.NativeObject;
+        if (group.Properties["member"].Contains(userDn))
+        {
+            return;
+        }
+
+        group.Properties["member"].Add(userDn);
+        group.CommitChanges();
+        logger.LogInformation(
+            BrokerEventIds.DirectoryRoleGroupMembershipAdded,
+            "Added {InstitutionalUser} with role {Role} to Active Directory security group {GroupDn}.",
+            identity.UserName,
+            identity.Role,
+            groupDn);
+    }
+
     private void TryEnsureRemoteDesktopGroupMembership(DirectoryEntry user, string institutionalUser)
     {
         if (string.IsNullOrWhiteSpace(options.RemoteDesktopGroupDn))