In this web development project using EJS, MongoDB, Node.js, and Express.js, I prioritized robust authentication and security measures. I implemented user authentication with Passport.js, incorporating strategies like OAuth and local authentication. For MongoDB security, I followed best practices including input validation, error handling, and prepared statements to prevent injection attacks. Role-based access control (RBAC) was enforced to restrict user privileges and ensure data confidentiality. Secure communication with MongoDB was maintained using encrypted connections. Node.js and Express.js played a crucial role in security by enabling middleware implementation for tasks like input validation, sanitization, and secure session management.