ASP.NET - Custom Policy Handlers

Custom policy handlers in ASP.NET Core are used to implement fine-grained authorization logic that goes beyond simple role or claim checks. They allow applications to decide access based on custom rules, business conditions or multiple claim combinations rather than relying only on predefined roles.

What Authorization Policies Are

An authorization policy is a named set of rules that determines whether a user is allowed to access a resource. Policies are evaluated after authentication and are enforced during authorization. They can include requirements such as specific claims, roles or custom logic.

Why Custom Policy Handlers Are Needed

Built-in authorization checks are limited to simple comparisons. Real applications often need more control, such as verifying ownership of data, checking subscription status or validating multiple conditions together. Custom policy handlers provide a way to implement this logic cleanly and consistently.

Role of a Policy Handler

A policy handler is responsible for evaluating a requirement defined in a policy. It receives the user’s identity information and contextual data and decides whether the requirement is satisfied. If the handler succeeds, authorization continues; otherwise, access is denied.

Where Policy Handlers Run in the Flow

Custom policy handlers run after authentication and after role or claim transformation, but before the endpoint logic executes. This ensures that all transformed claims and roles are available when authorization decisions are made.

Common Use Cases

Policy handlers are commonly used to enforce rules like “user can edit only their own data,” “access allowed only during business hours,” or “premium feature access based on subscription level.” These checks depend on logic rather than static identity values.

Design and Security Benefits

Custom policy handlers keep authorization logic centralized and reusable. Instead of placing access checks inside controllers or endpoints, policies enforce rules consistently across the application. This improves maintainability, reduces duplication and strengthens security by avoiding scattered authorization code.

How It Fits into Real Applications

In real systems, authentication confirms who the user is, claim transformation adapts identity data and custom policy handlers enforce application-specific access rules. Together, they create a flexible and secure authorization pipeline suitable for complex enterprise and API-based applications.