This guide provides a comprehensive overview of API authentication and authorization, explaining the difference between the two concepts and how they work together to ensure secure API access. It covers various authentication methods, including basic authentication, API key authentication, JSON Web Tokens (JWT), OAuth 2.0, and OpenID Connect, discussing their strengths, weaknesses, and use cases. The guide also emphasizes the importance of token management, monitoring, logging, and performance optimization in API security. Additionally, it highlights the benefits of using a headless CMS like Strapi v5 for robust authentication features, including support for local and third-party providers, Role-Based Access Control (RBAC) system, and secure authorization using JWT tokens. The guide concludes by emphasizing the need for ongoing security measures and encouraging readers to prioritize API security to protect their data, users, and organization's reputation.