use this package socket.io for real-time notifications
Setup socket server on the backend
Setup client connection (should connect if the user is authed - see code below)
We also want an object to keep track of which users are currently connected - using a service, a database like Redis, or we can for now just use an in-memory variable (not recommended for the future, but it works for this project)
const cache = {}; (works for single instance)
io.on('connect', (socket)=>{
socket.headers.cookies[''] // can do some validation here
socket.disconnect()
})