auth.js

// middleware/auth.js
// Protects routes by verifying the JWT sent in the Authorization header,
// and provides role-based access control.

const jwt = require('jsonwebtoken');
const asyncHandler = require('express-async-handler');
const User = require('../models/User');

// Verifies the bearer token and attaches the authenticated user to req.user
const protect = asyncHandler(async (req, res, next) => {
  let token;

  if (req.headers.authorization && req.headers.authorization.startsWith('Bearer')) {
    try {
      token = req.headers.authorization.split(' ')[1];
      const decoded = jwt.verify(token, process.env.JWT_SECRET);

      req.user = await User.findById(decoded.id).select('-password');
      if (!req.user) {
        res.status(401);
        throw new Error('User no longer exists');
      }
      return next();
    } catch (error) {
      res.status(401);
      throw new Error('Not authorized, token invalid or expired');
    }
  }

  res.status(401);
  throw new Error('Not authorized, no token provided');
});

// Restricts a route to a set of allowed roles, e.g. authorize('admin', 'agent')
const authorize = (...roles) => {
  return (req, res, next) => {
    if (!req.user || !roles.includes(req.user.role)) {
      res.status(403);
      throw new Error(`Role '${req.user ? req.user.role : 'guest'}' is not permitted to access this resource`);
    }
    next();
  };
};

module.exports = { protect, authorize };