OF-2397: Do not process subscription requests for shared contacts

When a contact is a contact by virtue of being in a shared group, the presence subscription between the roster owner and this contact is deemed to be static.

Presence subscriptions sent by the client of either party should not affect this status.

xmppserver/src/main/java/org/jivesoftware/openfire/handler/PresenceSubscribeHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2004-2008 Jive Software, 2017-2023 Ignite Realtime Foundation. All rights reserved.
+ * Copyright (C) 2004-2008 Jive Software, 2017-2024 Ignite Realtime Foundation. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -299,6 +299,9 @@ private boolean manageSub(JID target, boolean isSending, Presence presence, Rost
         try {
             if (roster.isRosterItem(target)) {
                 item = roster.getRosterItem(target);
+                if (item.isShared()) {
+                    throw new SharedGroupException("Target '" + target + "' is on the roster of '" + roster.getUsername() + "' as part of a shared group. As such, its presence subscription status cannot be modified with subscription requests.");
+                }
             }
             else {
                 if (Presence.Type.unsubscribed == type || Presence.Type.unsubscribe == type ||