Demystifying Microsoft.AspNetCore.Authorization

Introduction

Authorization is a critical aspect of any web application, as it ensures that users can only access the resources they are allowed to. Microsoft’s ASP.NET Core framework offers a powerful and flexible authorization system through the Microsoft.AspNetCore.Authorization namespace. In this article, we will delve into the key components of this system, examine how it works, and explore various ways to implement custom authorization policies.

Overview of Authorization in ASP.NET Core

ASP.NET Core provides a built-in authorization system that enables developers to secure their applications easily. This system is based on three main components: policies, requirements, and handlers. Policies are a set of rules that define which users can access specific resources. Requirements are individual components of a policy, and handlers are responsible for evaluating if the requirements are met.

The Microsoft.AspNetCore.Authorization namespace contains several classes and interfaces that developers can use to create and manage their authorization rules. Some of the primary classes include:

• IAuthorizationService: The main service for authorization, responsible for evaluating if a user meets the requirements of a specific policy.
• AuthorizationPolicy: A class representing a collection of authorization requirements.
• IAuthorizationRequirement: An interface representing a single authorization requirement.
• AuthorizationHandler<TRequirement>: A base class for creating custom handlers for specific authorization requirements.

Implementing Authorization Policies

Role-Based Authorization

One of the simplest ways to implement authorization is by using role-based authorization. In this approach, access to resources is granted based on the roles assigned to users. For example, you might have an “Admin” role that grants access to administrative features, and a “User” role that only grants access to basic app functionality.

To use role-based authorization, you need to create an authorization policy that specifies the required role(s). You can achieve this with the following code:

services.AddAuthorization(options =>
{
    options.AddPolicy("AdminOnly", policy => policy.RequireRole("Admin"));
});

You can then apply this policy to a controller or action method using the [Authorize] attribute:

[Authorize(Policy = "AdminOnly")]
public IActionResult AdminDashboard()
{
    return View();
}

Users who are not in the “Admin” role will be denied access to the AdminDashboard action.

Custom Authorization Requirements and Handlers

In some cases, role-based authorization may not be sufficient for your application’s needs. You may need to implement custom authorization logic based on specific application conditions. In this case, you can create custom requirements and handlers.

First, define a custom requirement by implementing the IAuthorizationRequirement interface:

public class MinimumAgeRequirement : IAuthorizationRequirement
{
    public int MinimumAge { get; }

    public MinimumAgeRequirement(int minimumAge)
    {
        MinimumAge = minimumAge;
    }
}

Next, create a handler for the custom requirement by extending the AuthorizationHandler<TRequirement> class:

public class MinimumAgeHandler : AuthorizationHandler<MinimumAgeRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context,
                                                   MinimumAgeRequirement requirement)
    {
        var dateOfBirthClaim = context.User.FindFirst(claim => claim.Type == "DateOfBirth");

        if (dateOfBirthClaim != null)
        {
            var dateOfBirth = DateTime.Parse(dateOfBirthClaim.Value);
            var age = DateTime.Today.Year - dateOfBirth.Year;

            if (age >= requirement.MinimumAge)
            {
                context.Succeed(requirement);
            }
        }

        return Task.CompletedTask;
    }
}

Now, register the custom handler and create a policy that uses the custom requirement:

services.AddSingleton<IAuthorizationHandler, MinimumAgeHandler>();

services.AddAuthorization(options =>
{
    options.AddPolicy("AtLeast18YearsOld", policy =>
        policy.Requirements.Add(new MinimumAgeRequirement(18)));
});

Finally, apply the custom policy to a controller or action method:

[Authorize(Policy = "AtLeast18YearsOld")]
public IActionResult AdultContent()
{
    return View();
}

Conclusion

The Microsoft.AspNetCore.Authorization namespace provides a powerful and flexible way to implement authorization in ASP.NET Core applications. By combining built-in role-based authorization with custom requirements and handlers, you can create a secure and tailored authorization system that meets your application’s unique needs.