payment gateway using socket.io and nodejs - angularjs

Question

I am developing a payment gateway (with 2 factor authorization, 2FA) with node/express for server side and angular js for client side.
The communication from client --> server can be done via a POST request but I want the communication from server --> client to happen via socket.io.
Now for new user who initiates a payment, a POST request will be sent from the client to server, data will be processed and a response will be sent back. For a very very specific reason, the response cannot be sent as part of the res in the received POST request.
app.post('/receive', function(req,res){
data = req.body
res.send('success')
// do something with the data
// Details regarding 2FA will be sent later via socket.io
}
After some processing, data will be sent to the client regarding 2 factor authorization.
io.on('2fa', {name:name, oneTimePassword:qwerty //and additional details})
I can listen to the channel 2fa from the client side, but every message emited on this will go to all the clients. I need a way to send a message to specific clients only who initiate that particular payment process.
Each transaction will be encrypted using ECDH. A UUID will be available for the transaction, initiating customer as well as the order number for which the payment is being done.
Appreciate any guidance for the above.

Answer 1

Socket.io has rooms. If you want, let's say, only the buyer and the seller to hear about the authentication result, put them into a room and emit your messages to the room itself. The client side won't change. You just socket.emit from the client to the server and the server will put the client into a room with all other appropriate parties and all the subsequent communication will only be emitted to the room instead of the channel 2fa.
This is from an html5 multiplayer game I developed, when the client joins a game room, this is what happens on the server side:
socket.on('joingame', function(data){
if(livingplayers[data.room] && livingplayers[data.room][data.id]){
socket.emit('joinfail', 'That name is taken');
} else {
socket.join(data.room);
socket.emit('joingame', data);
}
});
So, as you can see here, I join the client into the game, and I responded from the same channel and I informed the client that he successfully joined the game and on the server side I put the client into the room he joined. Any subsequent in-game actions will be broadcasted only to the room that the client just joined here.