problem with load balancer session cookies with socket io client

[tmarinov82]

Hello again,
in the same setup from discussion "change the default port 8080 of socket io to different port #4876" we experience a problem with load balancer session cookies with the socket io client used in react front end. We host socket io application in Linux Azure Web App. The web app has 2 instances. There is a load balancer in the Azure web app where we can only use session cookies produced from the LB. Based on the session cookies the load balancer send the subsequent requests to the same hosts. In the browser development tools we see 5 request send from socket io client to the LB:

The expected behavior would be that a cookie has been set in the first request which is received from the browser to be sent in the next 4 requests, but this didn't happen, maybe because the requests are sent from the socket io client. All the next 4 requests are sent without the cookie which is received from the first request and as a result the requests are sent to different hosts and each of them receive a different cookie from the LB.
We also try to sent a cookie from socket io server for the test with the following configuration:
let io = new Server(httpServer, {
cookie: {
name: "io",
path: "/",
httpOnly: false,
sameSite: "none"
},
cors: {
origin: 'http://localhost:3000',
credentials: true
}
});
The idea was to sent a cookie without http only flag.
We tried to implement at the client the solution from https://socket.io/how-to/deal-with-cookies
socket.io.on("open", () => {
socket.io.engine.transport.on("pollComplete", () => {
const request = socket.io.engine.transport.pollXhr.xhr;
const headers = request.getAllResponseHeaders();
const cookieHeader = request.getResponseHeader("set-cookie");
console.log(headers , cookieHeader )
});
});
but the cookieheader is missing. We see only the following headers:
cache-control: no-store
content-length: 118
content-type: text/plain; charset=utf-8
So we cannot set the cookie received from the first request to the next through this solution.

[tmarinov82]

On socket io client side adding withCredentials: true does the trick.

import io from "socket.io-client"
const socket = io.connect('socket io server', {
withCredentials: true
});