req.session.user gives 'undifined' as output - mongodb

Question

I am implementing a login authentication program in MERN stack.
When I enter correct user name and password, login function works fine.
There are some components which can be displayed only if the client is logged in. Therefore, to validate the client I have implemented authenticator function in the server which should return success message along with the session object.
Once I try to authenticate, req.session.user gives the output as 'undefined'. I referred several similar questions but couldn't solve my issue.How can I solve this issue?
Login function,
router.post('/login', (req, res) => {
const email = req.body.email;
const password = req.body.password;
if (!email || !password) {
return res.status(400).json({ msg: "Please enter all fields" });
}
//Find user
User.findOne({ email : email })
.then(user => {
if(!user){
console.log('Not a user')
}
//Password matching
bcrypt.compare(password, user.password, (err, isMatch) => {
if(err) throw err;
if(isMatch){
console.log('Logged in')
const userSession = {
id: user.id,
name : user.name,
email : user.email
};
req.session.user = userSession;
res.json({ msg: "Logged in successfully", userSession});
} else {
console.log('Incorrect username or password')
}
});
})
.catch(err => console.log(err));
});
server.js,
const express = require('express');
const expressLayouts = require('express-ejs-layouts');
const mongoose = require('mongoose');
const passport = require('passport');
const flash = require('connect-flash');
const session = require('express-session');
const cors = require('cors');
const MongoDBStore = require('connect-mongodb-session')(session);
const app = express();
const router = express.Router();
const {IS_PROD} = require('./config/config');
const MAX_AGE = 1000 * 60 * 2;
mongoose.connect("mongodb+srv://root:admin#cluster0-ynman.gcp.mongodb.net/test?retryWrites=true&w=majority", {useNewUrlParser:true, useCreateIndex:true, useUnifiedTopology:true})
.then(() => console.log('Mongo DB Connected'))
.catch(err => console.log(err));
//setting up connect-mongodb-session store
const mongoDBStore = new MongoDBStore({
uri: "mongodb+srv://root:admin#cluster0-ynman.gcp.mongodb.net/test?retryWrites=true&w=majority",
collection : "mySession"
})
//Bodyparser
app.use(express.urlencoded({extended:false}));
app.use(cors());
app.use(express.json());
//Express Session
app.use(session({
name: 'session',
secret: 'secret',
resave: true,
saveUninitialized: false,
store : mongoDBStore,
cookie :{
path : '/',
httpOnly: false,
maxAge : MAX_AGE,
sameSite: false,
secure : IS_PROD
}
}));
//Routes
app.use('/', require('./routes/index'));
app.use('/users', require('./routes/users'));
const PORT = process.env.PORT || 5000;
app.listen(PORT, console.log(`Server starts on port ${PORT}`));
Authenticate funtion,
router.get("/authenticator", (req, res) => {
const userSession = req.session.user;
console.log(userSession);
if(userSession){
return res.json({msg : "Authenticated successfully", userSession});
} else {
return res.status(401).json({msg : "Unauthorized"});
}
});