Is it possible to send Push Notification messages from another client directly?

Question

The question is as follows:

1. User A registers with PushSubscription to get an endpoint URL and sends it to my server.
2. User B receives the endpoint URL of user A from my server.
3. User B send some message in HTTP method to its endpoint URL of user A - and that happend without it going through my server!

Is it possible or i missing something?