Proactively identify and mitigate API security risks using practical testing techniques in an ASP.NET Core development workflow. With APIs becoming the backbone of modern applications and digital transformation, they have also become prime targets for cyberattacks. This book empowers you to take control of your API security by integrating security testing directly into your development process. Through hands-on C# code examples using WebApplicationFactory and real-world scenarios from a vulnerable Banking API, you will learn to write security tests that verify your defenses against each of the OWASP Top 10 API Security risks. From broken authorization and authentication flaws to server-side request forgery and security misconfiguration, each chapter provides concrete testing strategies that catch vulnerabilities before they reach production. By following the testing patterns and practices presented in this book, you will build APIs that are not just functional but comprehensively secure. What You Will Learn Write security-focused integration tests using WebApplicationFactory and C# that integrate seamlessly into your development workflow Test and defend your APIs against all OWASP Top 10 API Security risks, including broken authorization, authentication bypass, and injection vulnerabilities Integrate API security testing as a natural part of the ASP.NET Core API development process Build a security mindset that treats security as a fundamental quality attribute of your APIs Who This Book is For This book is for ASP.NET Core developers, QA engineers, and DevOps professionals who want to take ownership of API security testing. Whether you are building new APIs or securing existing ones, you will benefit from the practical testing techniques presented here. Familiarity with C# and basic ASP.NET Core development is assumed, but no prior security expertise is required. This is an evergreen book that is not specific to any particular version of ASP.NET Core.