How to Use DelegatingHandler to Build Middleware Pipelines for HttpClient in .NET

The DelegatingHandler class in .NET's HttpClient allows developers to build a chain of interceptors that process every HTTP request and response in sequence. Modeled after the Chain of Responsibility design pattern, each handler in the pipeline can inspect or modify requests before passing them along, and responses on the way back. Practical use cases include logging request durations, automatically injecting authentication tokens, propagating correlation IDs across microservices, and recording performance metrics. Multiple handlers can be registered and chained together using the IHttpClientFactory configuration in the dependency injection setup. This approach centralizes cross-cutting concerns and eliminates repetitive boilerplate code scattered across HTTP call sites.