kickstart-express/templates/add/auth/jwt/ts/middleware/auth.ts

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import jwt from 'jsonwebtoken';
import { Request, Response, NextFunction } from 'express';

interface AuthenticatedRequest extends Request {
  user?: any;
}

/**
 * JWT Authentication Middleware
 * Validates JWT tokens and attaches user information to the request
 */
const authMiddleware = (req: AuthenticatedRequest, res: Response, next: NextFunction) => {
  try {
    // Get token from Authorization header
    const authHeader = req.headers.authorization;
    
    if (!authHeader || !authHeader.startsWith('Bearer ')) {
      return res.status(401).json({ 
        error: 'Access denied. No token provided or invalid format.' 
      });
    }

    const token = authHeader.substring(7); // Remove 'Bearer ' prefix

    // Verify token
    const decoded = jwt.verify(token, process.env.JWT_SECRET as string);
    
    // Attach user information to request
    req.user = decoded;
    
    next();
  } catch (error: any) {
    if (error.name === 'TokenExpiredError') {
      return res.status(401).json({ error: 'Token has expired.' });
    }
    if (error.name === 'JsonWebTokenError') {
      return res.status(401).json({ error: 'Invalid token.' });
    }
    return res.status(500).json({ error: 'Token verification failed.' });
  }
};

export default authMiddleware;