diff --git a/src/service-worker.template.js b/src/service-worker.template.js
index af8eae88..2a246737 100644
--- a/src/service-worker.template.js
+++ b/src/service-worker.template.js
@@ -68,18 +68,6 @@ self.addEventListener('fetch', (event) => {
     event.respondWith(handleRequest(event.request));
 });
 
-self.addEventListener('message', (event) => {
-    const reply = content => event.source.postMessage({replyTo: event.data?.id, content});
-    switch (event.data?.type) {
-        case "version":
-            reply({version: VERSION, buildHash: GLOBAL_HASH});
-            break;
-        case "skipWaiting":
-            self.skipWaiting();
-            break;
-    }
-});
-
 async function handleRequest(request) {
     const baseURL = self.registration.scope;
     if (request.url === baseURL) {
@@ -131,3 +119,52 @@ async function readCache(request) {
     }
     return response;
 }
+
+self.addEventListener('message', (event) => {
+    const reply = payload => event.source.postMessage({replyTo: event.data.id, payload});
+    const {replyTo} = event.data;
+    if (replyTo) {
+        const resolve = pendingReplies.get(replyTo);
+        if (resolve) {
+            pendingReplies.delete(replyTo);
+            resolve(event.data.payload);
+        }
+    } else {
+        switch (event.data?.type) {
+            case "version":
+                reply({version: VERSION, buildHash: GLOBAL_HASH});
+                break;
+            case "skipWaiting":
+                self.skipWaiting();
+                break;
+            case "closeSession":
+                event.waitUntil(
+                    closeSession(event.data.payload.sessionId, event.source.id)
+                        .then(() => reply())
+                );
+                break;
+        }
+    }
+});
+
+
+async function closeSession(sessionId, requestingClientId) {
+    const clients = await self.clients.matchAll();
+    await Promise.all(clients.map(async client => {
+        if (client.id !== requestingClientId) {
+            await sendAndWaitForReply(client, "closeSession", {sessionId});
+        }
+    }));
+}
+
+const pendingReplies = new Map();
+let messageIdCounter = 0;
+function sendAndWaitForReply(client, type, payload) {
+    messageIdCounter += 1;
+    const id = messageIdCounter;
+    const promise = new Promise(resolve => {
+        pendingReplies.set(id, resolve);
+    });
+    client.postMessage({type, id, payload});
+    return promise;
+}