When it comes to implementing authorization in ASP.NET Core, developers often rely on declarative authorization using the [Authorize] attribute. However, this approach has its limitations, particularly in scenarios where the evaluation of authorization must occur after the resource is retrieved from the data store. In such cases, a custom authorization method, also known as an imperative approach, is necessary. This is where resource-based authorization comes into play, providing a fine-grained access control approach to resources in ASP.NET Core.

In attribute-based authorization, the built-in authorization middleware of ASP.NET Core reads the [Authorize] attribute specified on the action methods of API controllers to determine if the requested action can be authorized for the current user. However, this approach has a caveat - the authorization middleware is executed before any action method or page handler is executed, which means it doesn't have access to the data on which the requested action method is supposed to run. This limitation is overcome by resource-based authorization, which attaches access control policies directly to specific resources like files, databases, APIs, and even cloud services.

In resource-based authorization, the focus is on the resource itself, rather than the user's identity, roles, or claims. This approach identifies who (users, roles, or other services) can perform specific actions on the resource. For instance, in a document editing scenario, only the document's author or creator is authorized to edit or delete it, while other users can only view the document. Resource-based authorization allows or denies access to particular resources based on specified requirements of those resources, i.e., policies, and the user's permissions.

To implement resource-based authorization in ASP.NET Core, developers can create an ASP.NET Core Web API project and define a resource, such as an instance of the Article class. A repository is then created to provide access to the data store, and an authorization handler is implemented to determine if the user has access to a particular resource. The authorization handler is registered with the dependency injection container, and one or more authorization policies are defined. Finally, a controller is created to expose action methods to access resources, and the instance of type IAuthorizationService is used to validate if the user has access to edit the article.

The implementation of resource-based authorization in ASP.NET Core provides a more fine-grained access control approach to resources, particularly in scenarios where declarative authorization is not sufficient. While this approach requires more effort and complexity, it offers a more robust and flexible way to manage access to resources in ASP.NET Core applications.

In conclusion, resource-based authorization is a powerful tool in ASP.NET Core that enables developers to provide fine-grained access control to resources in scenarios not supported by attribute-based authorization. By understanding the limitations of declarative authorization and the benefits of resource-based authorization, developers can create more secure and robust ASP.NET Core applications.