Index: binaries/data/config/default.cfg
===================================================================
--- binaries/data/config/default.cfg
+++ binaries/data/config/default.cfg
@@ -525,6 +525,7 @@
 name_id = "0ad"
 
 [network]
+allowlist = everyone              ; Allow certain players to join the game. Possible values: everyone, buddies.
 duplicateplayernames = false      ; Rename joining player to "User (2)" if "User" is already connected, otherwise prohibit join.
 lateobservers = everyone          ; Allow observers to join the game after it started. Possible values: everyone, buddies, disabled.
 observerlimit = 8                 ; Prevent further observer joins in running games if this limit is reached
Index: binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
===================================================================
--- binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
+++ binaries/data/mods/public/gui/gamesetup_mp/gamesetup_mp.js
@@ -165,6 +165,7 @@
 	case "not_server": return translate("Server is not running.");
 	case "invalid_password": return translate("Password is invalid.");
 	case "banned": return translate("You have been banned.");
+	case "not_allowed": return translate("You are not allowed to join this game. Ask the hoster how you can be added to the allow-list.");
 	case "local_ip_failed": return translate("Failed to get local IP of the server (it was assumed to be on the same network).");
 	default:
 		warn("Unknown connection failure reason: " + reason);
Index: binaries/data/mods/public/gui/options/options.json
===================================================================
--- binaries/data/mods/public/gui/options/options.json
+++ binaries/data/mods/public/gui/options/options.json
@@ -559,6 +559,16 @@
 			},
 			{
 				"type": "dropdown",
+				"label": "Player joins (allow-list)",
+				"tooltip": "Allow everyone or buddies only to join the game.",
+				"config": "network.allowlist",
+				"list": [
+					{ "value": "everyone", "label": "Everyone" },
+					{ "value": "buddies", "label": "Buddies" }
+				]
+			},
+			{
+				"type": "dropdown",
 				"label": "Late observer joins",
 				"tooltip": "Allow everybody or buddies only to join the game as observer after it started.",
 				"config": "network.lateobservers",
Index: source/lobby/XmppClient.cpp
===================================================================
--- source/lobby/XmppClient.cpp
+++ source/lobby/XmppClient.cpp
@@ -1,4 +1,4 @@
-/* Copyright (C) 2021 Wildfire Games.
+/* Copyright (C) 2023 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -975,6 +975,17 @@
 				m_client->send(response);
 				return true;
 			}
+			if (!g_NetServer->IsUserInAllowList(iq.from().username()))
+			{
+				glooxwrapper::IQ response(gloox::IQ::Result, iq.from(), iq.id());
+				ConnectionData* connectionData = new ConnectionData();
+				connectionData->m_Error = "not_allowed";
+
+				response.addExtension(connectionData);
+
+				m_client->send(response);
+				return true;
+			}
 			if (!g_NetServer->CheckPasswordAndIncrement(iq.from().username(), cd->m_Password.to_string(), cd->m_ClientSalt.to_string()))
 			{
 				glooxwrapper::IQ response(gloox::IQ::Result, iq.from(), iq.id());
@@ -1013,6 +1024,8 @@
 
 			response.addExtension(connectionData);
 
+			LOGMESSAGE("XmppClient: Sent connection data including public IP address to %s", iq.from().username());
+
 			m_client->send(response);
 		}
 
Index: source/network/NetServer.h
===================================================================
--- source/network/NetServer.h
+++ source/network/NetServer.h
@@ -1,4 +1,4 @@
-/* Copyright (C) 2022 Wildfire Games.
+/* Copyright (C) 2023 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -183,6 +183,14 @@
 	 */
 	bool IsBanned(const std::string& username) const;
 
+	/**
+	 * Check if user is allowed by the overall server policy (e.g. invite only).
+	 * This function is used by XmppClient to check whether the username
+	 * is allowed. If not then the server's public IP address is not sent to
+	 * the lobby user
+	 */
+	static bool IsUserInAllowList(const std::string& username);
+
 	void SetPassword(const CStr& password);
 
 	void SetControllerSecret(const std::string& secret);
Index: source/network/NetServer.cpp
===================================================================
--- source/network/NetServer.cpp
+++ source/network/NetServer.cpp
@@ -195,6 +195,35 @@
 	delete m_ServerTurnManager;
 }
 
+bool CNetServer::IsUserInAllowList(const std::string& username)
+{
+	CStrW theUsername(wstring_from_utf8(username));
+	CStrW usernameWithoutRating(theUsername.LowerCase().substr(0, theUsername.find(L" (")));
+	// Check whether the allow-list is set to buddies only
+	CStr allowListSetting;
+	CFG_GET_VAL("network.allowlist", allowListSetting);
+
+	if (allowListSetting != "buddies")
+		// All users are allowed.
+		return true;
+
+	CStr buddies;
+	CFG_GET_VAL("lobby.buddies", buddies);
+	std::wstringstream buddiesStream(wstring_from_utf8(buddies));
+	CStrW buddy;
+	while (std::getline(buddiesStream, buddy, L','))
+	{
+		if (buddy.LowerCase() == usernameWithoutRating)
+		{
+			// User found in allow list.
+			return true;
+		}
+	}
+
+	// User not found in allow list.
+	return false;
+}
+
 void CNetServerWorker::SetPassword(const CStr& hashedPassword)
 {
 	m_Password = hashedPassword;