diff --git a/CHANGELOG.md b/CHANGELOG.md
index e4f7f7f4..a0dfdd58 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,3 +16,11 @@ Version 2.0.0
 - The masterIP and masterPort config entries has been merged into masterURL.
   Breaks discordChat, playerManager, serverSelect, trainTeleports and
   clusterioModel.
+
+
+Version 1.2.1
+-------------
+
+### Breaking Changes
+
+- Added authentication to the socket.io server running on the master.
diff --git a/client.js b/client.js
index 5d45d69b..cf62972d 100644
--- a/client.js
+++ b/client.js
@@ -603,7 +603,10 @@ async function instanceManagement(instanceconfig) {
     console.log("Started instanceManagement();");
 
     /* Open websocket connection to master */
-	var socket = ioClient(config.masterURL);
+	var socket = ioClient(config.masterURL+"?token="+config.masterAuthToken);
+	socket.on("error", err => {
+		console.log("SOCKET | Error: ", err);
+	});
 	socket.on("hello", data => {
 		console.log("SOCKET | registering slave!");
 		socket.emit("registerSlave", {
diff --git a/master.js b/master.js
index 6e86dd4e..8fab7728 100644
--- a/master.js
+++ b/master.js
@@ -756,6 +756,18 @@ class wsSlave {
 	}
 }
 
+io.use((socket, next) => {
+	let token = socket.handshake.query.token;
+	authenticate.check(token).then((result) => {
+		if (result.ok) {
+			next();
+		} else {
+			console.error(`SOCKET | authentication failed for ${socket.handshake.address}`);
+			next(new Error(result.msg));
+		}
+	});
+});
+
 io.on('connection', function (socket) {
 	// cleanup dead sockets from disconnected people
 	let terminatedConnections = 0;