Introduction

One of the cornerstones of web application security is ensuring that only the right people have access to the right resources. But what is authorization, and why is it pivotal in web security? In essence, authorization is the process by which a server determines if the client has permission to access a resource or execute a function. It’s the system’s way of saying, “You’re allowed (or not allowed) to do this.” With the evolution of ASP.NET to its 7.0 version, this is achieved through a powerful tool called “authorization policies”. In this article, we’ll break down what these policies are, why they matter, and how to use them effectively.

What are Authorization Policies?
Authorization policies in ASP.NET are sets of requirements that dictate who can access certain resources. These policies can be based on user roles, claims, or even custom rules you establish.

Setting up the Basics:
Before you delve into policies, ensure you have the necessary services registered. In Startup.cs or Program.cs:

services.AddAuthorization();

Creating a Simple Policy:
For instance, limiting actions to users with an “Admin” role is straightforward:

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

// Using the policy in a controller:
[Authorize(Policy = "RequireAdminRole")]
public IActionResult AdminDashboard()
{
    return View();
}

Using Claims in Policies:
Policies can also be based on user claims. Let’s consider an example where access is restricted based on age:

1. Defining the Policy:
   This is where you’ll introduce logic to verify age:

services.AddAuthorization(options =>
{
    options.AddPolicy("Over18Only", policy => 
        policy.RequireClaim(ClaimTypes.DateOfBirth, /* here you'd typically check if the date of birth claim suggests an age over 18 */));
});

(Note to readers: For simplification, the logic to check age isn’t included in the snippet above, but in a real-world scenario, you’d typically evaluate the DateOfBirth claim against the current date to deduce age.)

Custom Requirements:
ASP.NET 7.0 enables you to create custom policy requirements. Let’s explore the WeekdayOnlyRequirement:

1. Creating the Requirement:
   Start by creating a new requirement class:

public class WeekdayOnlyRequirement : IAuthorizationRequirement { }

The WeekdayOnlyRequirement class, in this scenario, acts as a marker. It doesn’t contain any logic but signals what kind of authorization is required.

2. Crafting a Handler:
   Then, you’ll create a handler for this requirement:

public class WeekdayOnlyHandler : AuthorizationHandler<WeekdayOnlyRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, WeekdayOnlyRequirement requirement)
    {
        if (DateTime.Now.DayOfWeek != DayOfWeek.Saturday && DateTime.Now.DayOfWeek != DayOfWeek.Sunday)
        {
            context.Succeed(requirement);
        }

        return Task.CompletedTask;
    }
}

Here, the handler checks if the current day is a weekday. If it is, access is granted.

3. Registering and Applying:
   Finally, you’ll register this handler and attach the policy:

services.AddSingleton<IAuthorizationHandler, WeekdayOnlyHandler>();
services.AddAuthorization(options =>
{
    options.AddPolicy("WeekdayOnly", policy => policy.Requirements.Add(new WeekdayOnlyRequirement()));
});

Expanding on Use Cases:
Authorization policies can be molded to fit a plethora of scenarios. From time-based access, like the weekday example above, to more intricate cases like geolocation-based access or tiered user permissions, the flexibility of ASP.NET 7.0’s authorization policies provides a robust framework for web application security.

Conclusion:
Harnessing the power of authorization policies in ASP.NET 7.0 ensures your resources remain accessible to the right eyes and hands. As you traverse the realms of ASP.NET, let these policies guide your path to a secure and user-friendly application.