C# Web API Development

Your service works in the demo. Then real clients arrive with broken JSON, expired tokens and two customers buying the last item at once. This book builds one small online shop service on .NET 9 and takes it apart one concern at a time: the request pipeline, routing, minimal APIs and controllers, model binding and validation, dependency injection, configuration, data access with transactions, problem details error responses, JWT authentication and policy-based authorization, in-memory testing with the test host, and deployment behind a proxy. Every example was built and run, including the surprises that cost an afternoon, such as claim mapping that quietly turns a valid role into a 403. You finish with a service that fails early, explains its errors and can be released by someone else.