Websocket to Websocket proxy acts as the rendezvous server for the attacker and the malware, its usage is simple: each client can open a WebSocket by connecting to the server at a given path /<path>.
Every client connected to the same <path> will receive every message sent for the same <path>.
Every client connected to the same <path> can also send a message to everyone else subscribed to the same <path> simply by sending the message to the websocket to websocket proxy.