Express.js, how to pass jwt cookie to Socket.io?

Question

I have a login route that eventually create a jwt cookie named access_token. After the login the client will receive this cookie and will send it on every request. However I didn’t found a way to pass this cookie on to Socket.io.

Server side login route :

const login = async (req, res) => {
      const {email, password} = req.body
      const user = await UserModel.findOne({email})
      const isMatch = await user.checkPassword(password)
      if (isMatch) {
        const userToken = JwtService.createToken(user.id)
        return res.cookie("access_token", userToken, {
            httpOnly: true,
            secure: process.env.NODE_ENV === "production"
        }).status(200).json({user:user.toJSON(),message: 'login success'})

    }
 }

Socket :

this.io = new socketio.Server(expressServer, {cors: {origin: 'http://localhost:3000'}})
    this.io.use((socket,next)=>{
        console.log(socket.handshake.headers.cookie); // undefiend
        next()
    })

Client :

  this.socket = socketIOClient(process.env.SOCKET_BASE_URL, {auth: {userId}});

Server :

         import express, {RequestHandler} from 'express';
        import http from 'http'
        import cookieParser from "cookie-parser"
        import cors from 'cors';
        import {router} from '@router';
        import dotenv from 'dotenv'
        import mongoose from 'mongoose';
        import {SocketService} from "@services";
        
        const expressApp = express();
        
        const port = process.env.PORT || 3001;
        dotenv.config()
        
        expressApp.use(cors({
            origin: true,
            credentials: true
        }));
        expressApp.use(express.json() as RequestHandler);
        expressApp.use(cookieParser());
        expressApp.use('/', router)
        
        const httpServer = http.createServer(expressApp);
        new SocketService(httpServer)
        
        httpServer.listen(port, async () => {
            console.log(`server is listening on ${port}`);
            try {
               await mongoose.connect('mongodb://guess-it-mongo-dev:27017/guess-it', {connectTimeoutMS: 1000});
               console.log('connected to mongo server')
            } catch (e) {
                console.log(e);
            }
        });

Answer 1

1. Solution

Assuming that you have only one cookie which is your jwt, you could get it with the socket param like so :

const token = socket.handshake.headers.cookie.split("=")[1];

If you have many cookies, you need to use some cookie parser and give it the socket.handshake.headers.cookie to parse it, for example:

function getCookie(cName) {
   const name = cName + "=";
   const cDecoded = decodeURIComponent(socket.handshake.headers.cookie);
   const cArr = cDecoded.split(';');
   let res;
   cArr.forEach(val => {
      if (val.indexOf(name) === 0) res = val.substring(name.length);
      })
   return res;
}
const token = getCookie("jwt"); // if your token is called jwt.

2. Troubleshot

If the given solution is not working for you, make sure you are setting up your app and socket this way to have them as a single server (feel free to change the port):

const app = express();
const http = require("http");
const server = http.createServer(app);
const { Server } = require("socket.io");
const io = new Server(server);

server.listen(9000, () => {
   console.log("server runnig on port " + 9000);
});

And the client should be connecting like this (with the same port as the server) :

import { io } from "socket.io-client";

io("http://localhost:9000/", {
      transports: ["websocket"],
    });

3. An use case

For example, in the code below, I am authenticating every connection with a middleware:

io.use((socket, next) => {
const token = socket.handshake.headers.cookie.split("=")[1];
if (token) {
  jwt.verify(token, process.env.SECRET, (err, decodedToken) => {
    if (err) {
      next(new Error("invalid"));
    } else {
      User.findById(decodedToken.id, function (err, user) {
        if (err) {
          next(new Error("invalid"));
        } else {
          next();
        }
      });
    }
  });
} else {
  next(new Error("invalid"));
}
});

//if authentication is ok, the code below will get executed 
io.on("connection", (socket) => {
  // do things
})