server.js

// server.js
const serverless   = require('serverless-http');
const express      = require('express');
const cors         = require('cors');
const dotenv       = require('dotenv');
const passport     = require('passport');
const passportJWT  = require('passport-jwt');
const jwt          = require('jsonwebtoken');
const userService  = require('./user-service.js');

dotenv.config();

const ExtractJwt  = passportJWT.ExtractJwt;
const JwtStrategy = passportJWT.Strategy;
const jwtOptions  = {
  jwtFromRequest: ExtractJwt.fromAuthHeaderWithScheme('jwt'),
  secretOrKey:    process.env.JWT_SECRET
};

passport.use(new JwtStrategy(jwtOptions, (jwt_payload, next) => {
  if (jwt_payload && jwt_payload._id && jwt_payload.userName) {
    next(null, { _id: jwt_payload._id, userName: jwt_payload.userName });
  } else {
    next(null, false);
  }
}));

const app = express();
app.use(passport.initialize());
app.use(express.json());
app.use(cors());

app.post("/api/user/register", (req, res) => {
  userService.registerUser(req.body)
    .then(msg => res.json({ message: msg }))
    .catch(err => res.status(422).json({ message: err }));
});

app.post("/api/user/login", (req, res) => {
  userService.checkUser(req.body)
    .then(user => {
      const payload = { _id: user._id, userName: user.userName };
      const token   = jwt.sign(payload, process.env.JWT_SECRET, { expiresIn: '2h' });
      res.json({ message: 'login successful', token });
    })
    .catch(err => res.status(422).json({ message: err }));
});

const auth = passport.authenticate('jwt', { session: false });

app.get   ("/api/user/favourites",        auth, (req, res) => userService.getFavourites (req.user._id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));
app.put   ("/api/user/favourites/:id",    auth, (req, res) => userService.addFavourite   (req.user._id, req.params.id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));
app.delete("/api/user/favourites/:id",    auth, (req, res) => userService.removeFavourite(req.user._id, req.params.id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));
app.get   ("/api/user/history",           auth, (req, res) => userService.getHistory   (req.user._id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));
app.put   ("/api/user/history/:id",       auth, (req, res) => userService.addHistory     (req.user._id, req.params.id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));
app.delete("/api/user/history/:id",       auth, (req, res) => userService.removeHistory  (req.user._id, req.params.id).then(data => res.json(data)).catch(err => res.status(422).json({ error: err })));

//
// Connect to Mongo once at cold start, then export the handler
//
let connectPromise = userService.connect();

const handler = serverless(app);

module.exports = async (req, res) => {
  await connectPromise;
  return handler(req, res);
};