Best Practices for User Authentication and Authorization in Web Applications: A Comprehensive Security Framework

**Executive Summary:** This research paper provides a practical, cross-cutting framework for securing user authentication and authorization in web applications, covering modern password hashing (Argon2/bcrypt/PBKDF2), multi-factor and passwordless (WebAuthn) approaches, secure OAuth/OIDC usage, robust session management and cookie configurations, RBAC/ABAC/ReBAC authorization models, infrastructure and API protections (TLS, headers, rate limiting), and monitoring/response practices to detect and remediate credential-based threats while balancing security and usability.