Push Subscription Migrator

applicationServerKey transfer approach

When both origins share the same VAPID key pair (same applicationServerKey), some browsers allow the subscription endpoint to be reused at the new origin. This is the smoothest migration path.

// Step 1: Old origin - read current sub and include in migration push
const oldSub = await reg.pushManager.getSubscription();
const endpoint = oldSub.endpoint;
const p256dh = btoa(String.fromCharCode(...new Uint8Array(oldSub.getKey('p256dh'))));
const auth = btoa(String.fromCharCode(...new Uint8Array(oldSub.getKey('auth'))));

// Server sends push with migration payload:
// { migrateTo: 'https://new.example.com', endpoint, p256dh, auth }

// Step 2: New origin service worker - re-subscribe with same VAPID key
const newReg = await navigator.serviceWorker.ready;
const newSub = await newReg.pushManager.subscribe({
  userVisibleOnly: true,
  applicationServerKey: SAME_VAPID_PUBLIC_KEY,
});

// Step 3: Old SW unsubscribes
await oldSub.unsubscribe();