This book offers a comprehensive exploration of OpenID Connect (OIDC), the modern standard for secure user authentication and identity management. From foundational concepts to advanced implementation techniques, it provides a clear and practical guide to understanding OIDC's core principles, security mechanisms, and real-world applications. Readers will gain insight into the role of OIDC in Single Sign-On (SSO), API security, and cloud-based environments, as well as learn how to address common challenges and enhance system resilience. Designed for IT professionals, developers, and security experts, this book combines technical depth with actionable advice, empowering readers to confidently implement and manage OIDC in diverse environments.