Custom authorization policies and handlers?

Short answer: Define complex authorization rules using IAuthorizationHandler: public class MinimumAgeRequirement : IAuthorizationRequirement {

Example code

public int Age { get; }
public MinimumAgeRequirement(int age) => Age = age;
}
public class MinimumAgeHandler : AuthorizationHandler<MinimumAgeRequirement> { protected override Task HandleRequirementAsync(...) { // logic }
} Register in DI and use with [Authorize(Policy = "...")].

Real-world example (ShopNest)

A ShopNest checkout request flows through middleware, hits a minimal API or controller, uses scoped services, and returns ProblemDetails on errors.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.