create-auth-backend-cli/template/middlewares/auth.js

CLI to scaffold a Node.js Auth backend with Express, JWT, MongoDB

const jwt = require("jsonwebtoken");

/**
 * Middleware to verify JWT and optionally check user role
 * @param {Array<string>} allowedRoles - optional array of allowed roles
 */
const authMiddleware = (allowedRoles = []) => {
  return (req, res, next) => {
    const authHeader = req.headers.authorization;

    // 1. Check if header exists and starts with Bearer
    if (!authHeader || !authHeader.startsWith("Bearer ")) {
      return res.status(401).json({ error: "Authorization header missing or invalid" });
    }

    const token = authHeader.split(" ")[1];

    try {
      // 2. Verify token
      const decoded = jwt.verify(token, process.env.JWT_SECRET);
      req.user = decoded; // { id, role, iat, exp }

      // 3. Role-based access control (optional)
      if (allowedRoles.length > 0 && !allowedRoles.includes(decoded.role)) {
        return res.status(403).json({ error: "Access denied: insufficient permissions" });
      }

      next();
    } catch (err) {
      return res.status(401).json({ error: "Invalid or expired token" });
    }
  };
};

module.exports = authMiddleware;