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Explaining IAuthorizationFilter in .NET Core

In this article, we will cover ASP.NET Core IAuthorizationFilter.

Please refer to my previous article,

So, Let's get started.

What is the Authorization Filter?

The Authorization Filter allows us to apply authorization rules to controllers and actions within our application. Authorization Filters in ASP.NET Core are responsible for checking whether a user is allowed to perform an action or access a resource. These filters run before the action method is executed, ensuring the user has permission to access the method.

Authorization filters are executed after the routing but before model binding and other action filters. If the authorization fails (e.g., the user does not have the required permissions), the filter short-circuits the request, and the action method does not execute.

IAuthorizationFilter

In ASP.NET Core, IAuthorizationFilter is an interface that allows you to perform authorization checks on an action or a controller before the action executes. Implementing this interface gives you the ability to enforce security and authorization rules within your application.

Advantages of IAuthorizationFilter

  1. Centralized Authorization Logic: By using filters, you can centralize your authorization logic, making it easier to maintain and manage. You can apply the same filter to multiple controllers or actions.
  2. Separation of Concerns: Filters support the separation of concerns in your application. They promote clean architecture by isolating authorization logic from business logic.
  3. Flexibility: Since filters can be applied at the action or controller level, you have the flexibility to handle different authorization requirements for different endpoints easily.
  4. Access to Action Context: The `IAuthorizationFilter` provides access to the `ActionExecutingContext`, which contains information about the current request, the action is executed, and route data. This allows for dynamic authorization checks based on the context.
  5. Built-in to ASP.NET Core: It is part of the ASP.NET Core framework, which means it is well-integrated with the rest of the framework and benefits from the built-in dependency injection features.
  6. Chain of Responsibility: Multiple filters can be applied to a single action. This allows for a chain of responsibility pattern, where different filters can be called in a defined order.

Disadvantages of IAuthorizationFilter

  1. Performance Impact: If your authorization logic involves heavy or synchronous operations (like database calls), it can slow down request processing. This is critical if the logic is not optimized or you make external calls during authorization checks.
  2. Complexity in Conditional Logic: Complex authorization requirements that depend on various conditions may lead to complicated filter implementations, making it harder to read and maintain.
  3. Limited to Action Execution: Authorization filters are only executed before the action method is called. You cannot use them to enforce rules after action execution, such as in the response pipeline.
  4. Difficulty in Testing: If your authorization logic is embedded within the filters, unit testing may become more complex since you'll need to mock the entire filter environment.

Example

public class CustomAuthorizationFilter : IAuthorizationFilter
{
    public void OnAuthorization(AuthorizationFilterContext context)
    {
        // Implement your authorization logic here
        var user = context.HttpContext.User;

        if (!user.Identity.IsAuthenticated)
        {
            // User is not authenticated, return a 403 Forbidden response
            context.Result = new ForbidResult();
        }
    }
}
// Register the filter in Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddControllers(options =>
    {
        options.Filters.Add<CustomAuthorizationFilter>();
    });
}

// Above .net 6

builder.Services.AddScoped<CustomAuthorizationFilter>();
[ApiController]
[Route("[controller]")]
[ServiceFilter(typeof(CustomAuthorizationFilter))]
public class HomeController : ControllerBase
{
    [HttpGet]
    public IActionResult GetAuthorized()
    {
        return Ok("You are authorized!");
    }
}

Authorization

Forbidden

Swagger


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