How do you write a custom middleware? Create a class with: ● A constructor accepting RequestDelegate ● An Invoke or InvokeAsync method public class MyCustomMiddleware { private readonly RequestDelegate _next; public MyCustomMiddleware(RequestDelegate next) => _next = next; public async Task InvokeAsync(HttpContext context) { // Pre-processing logic

Answer: wait _next(context); // Post-processing logic } } Register it: pp.UseMiddleware<MyCustomMiddleware>();

What interviewers expect

• A clear definition tied to ASP.NET Core in ASP.NET Core projects
• Trade-offs (performance, maintainability, security, cost)
• When you would and would not use it in production

Real-world example

In a production ASP.NET Core application, teams apply this when handling user-facing features or integration boundaries. For example, you might use it during a sprint where reliability and observability matter—logging metrics, validating edge cases, and documenting the decision in an ADR so future developers understand why the approach was chosen.

How to explain in the interview

1. Define the concept in one or two sentences.
2. Context — where it fits in ASP.NET Core architecture.
3. Example — a specific project, bug, or performance win.
4. Trade-off — what you gain vs what you sacrifice.

Tip: Practice aloud on Toolliyo mock interview or the Interview Q&A section before your real interview.