Building secure REST APIs requires implementing multiple security layers. Start with HTTPS encryption using TLS certificates from Let's Encrypt or commercial providers. Implement authentication using JWT tokens with short expiration times and refresh token rotation. Use bcrypt for password hashing with appropriate salt rounds. Implement rate limiting with express-rate-limit to prevent brute force attacks. Validate all input using libraries like Joi or express-validator to prevent injection attacks. Set HTTP security headers using helmet middleware, including CSP, X-Frame-Options, and XSS-Protection. Implement CORS policies restricting allowed origins. Use parameterized queries or ORMs like Sequelize or Prisma to prevent SQL injection. Implement request size limits to prevent DoS attacks. Log security events without exposing sensitive data. Use environment variables for configuration, never hardcode secrets. Implement API versioning to manage breaking changes. Use HTTPS-only cookies for session management. Regular dependency updates with npm audit and Dependabot. Implement proper error handling that doesn't leak stack traces. Consider using API keys for service-to-service communication. Regular security audits and penetration testing complete your security posture.