I am trying to store information on my req.session object upon login and at a later time access this to verify if a user is logged in for middleware

I am aware there are several similar questions but after implementing their solutions, I am either unable to get any data to save on my session or I am unable to access it.

The solutions that I have seen on similar questions have been

1. Enabling cors on my express server
2. Setting the withCredentials parameter on my axios request to true
3. Calling session.save() after modifying my session

I should mention I am able to get this middleware function to work as desired with Postman which leads me to believe there is something wrong with how I am making my request.

I have the following signIn route

router.post('/signin', async (req, res) => {
  const {  email, password } = req.body;
  try {
    const user = await User.findOne({ email });
    if (!user) {
      return res.status(400).send('User not found');
    }

    const isMatch = await bcrypt.compare(password, user.hashedPassword);
    if (!isMatch) {
      return res.status(400).send('Invalid credentials');
    }

    const sessionUser = {
      id: user._id,
      email: user.email,
    }
  
    req.session.user = sessionUser;

    console.log('Sign in successful: ', email)
    req.session.save();
    res.status(200).send(req.session);

  } catch (err) {
    res.status(500).send('Error signing in');
  }
}

The following app.js file

const createError = require('http-errors');
const express = require('express');
const path = require('path');
const cookieParser = require('cookie-parser');
const logger = require('morgan');
const mongoose = require('mongoose');
const authRoutes = require('./routes/auth');
const newsletterRoutes = require('./routes/newsletter');
const session = require('express-session');
const MongoStore = require('connect-mongo');
const cors = require('cors');
require('dotenv').config();

const app = express();

app.use(cors(
    {
      origin: "http://localhost:3000",
      credentials: true,
    }
));

mongoose.connect('some_db_url');

const db = mongoose.connection;
db.on('error', console.error.bind(console, 'connection error:'));
db.once('open', function() {console.log('Connected to MongoDB');});

// Set up session middleware
app.use(session({
  secret: process.env.SESSION_SECRET,
  resave: false, // don't save session if unmodified
  saveUninitialized: false, // don't save session if there's nothing to save
  cookie: { maxAge: 24 * 60 * 60 * 1000 }, // Session cookie expiration (1 day)
  store: MongoStore.create({
    client: db.getClient(), // necessary option
    collectionName: 'sessions',
    autoRemove: 'true',
    stringify: 'false',
  })
}));

app.use(logger('dev'));
app.use(express.json());
app.use(express.urlencoded({ extended: false })); // parse application/x-www-form-urlencoded
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/auth', authRoutes);

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;

and on the frontend I have my handleSubmit function to sign in

const  handleSubmit = async (event) => {
        event.preventDefault();
        const data = new FormData(event.currentTarget);

        const payload = {
            email: data.get('email'),
            password: data.get('password'),
        }

        try {
            const response = await axios.post("http://localhost:8080/auth/signIn/", payload, {withCredentials: true});

            if (response.status === 200) {
                console.log('Login successful with ' + data);
            }
        } catch (error) {
            if (error.response.status === 400) {
                console.log('Invalid username or password');
            } else {
                console.error('Error while logging in', error);
            }
        }

    };

and lastly the following middleware function on my frontend

export const isLoggedIn = () => {

    try {
        const response = axios.get("http://localhost:8080/auth/check-auth/", {withCredentials: true});
        if (response.status === 200) {
            console.log('User authenticated, access granted')
            return true;
        }
    } catch (error) {
        if (error.response.status === 403) {
            console.log('403: User not authenticated, access denied')
            return false;
        } else {
            console.log('Unknown error while authenticating: ', error)
            return false;
        }
    }

}

In an attempt to access stored express-session data I enabled CORS on my express server and set withCredentials: true on axios requests from my frontend but my problem persists.