Advanced Authentication & Authorization

Mind Map Summary

• Topic: Advanced Authentication & Authorization
• Core Concepts:
  • Claims Transformation: The process of augmenting a user’s identity (ClaimsPrincipal) with additional claims after they have been authenticated. This is useful for adding roles, permissions, or other information from a database or external service.
  • Policy-Based Authorization: A declarative approach where authorization policies are registered at startup and then applied to endpoints. This decouples authorization logic from the application code.
    • Requirements: A collection of data parameters that a policy uses to evaluate a user’s identity.
    • Handlers: The logic that evaluates the requirements. A handler can be created for each requirement.
  • Federated Identity: Offloading authentication to an external identity provider (IdP) like Google, Azure AD, or IdentityServer. The application trusts the token issued by the IdP.
    • OpenID Connect (OIDC): A simple identity layer on top of the OAuth 2.0 protocol. It allows clients to verify the identity of the end-user based on the authentication performed by an Authorization Server.
• Pros:
  • Decoupling: Policy-based authorization separates authorization logic from business logic, making the code cleaner and easier to maintain.
  • Flexibility: Claims transformation allows for dynamic and flexible user identities.
  • Centralized Authentication: Federated identity centralizes user management and authentication, improving security and user experience.
• Cons:
  • Complexity: These concepts can be complex to set up and debug, especially for developers new to them.
  • External Dependencies: Federated identity introduces a dependency on an external IdP, which could be a point of failure.

Practice Exercise

Implement a custom authorization handler that checks for a specific condition, such as whether a user has been a member for more than a year (based on a RegistrationDate claim). Apply this policy to an API endpoint.

Answer

1. Define the Requirement:

using Microsoft.AspNetCore.Authorization;

public class MinimumMembershipRequirement : IAuthorizationRequirement
{
    public int MinimumYears { get; }

    public MinimumMembershipRequirement(int minimumYears)
    {
        MinimumYears = minimumYears;
    }
}

2. Create the Authorization Handler:

using Microsoft.AspNetCore.Authorization;
using System;
using System.Security.Claims;
using System.Threading.Tasks;

public class MinimumMembershipHandler : AuthorizationHandler<MinimumMembershipRequirement>
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, MinimumMembershipRequirement requirement)
    {
        var registrationDateClaim = context.User.FindFirst(c => c.Type == "RegistrationDate");

        if (registrationDateClaim != null && DateTime.TryParse(registrationDateClaim.Value, out var registrationDate))
        {
            if (registrationDate.AddYears(requirement.MinimumYears) < DateTime.UtcNow)
            {
                context.Succeed(requirement);
            }
        }

        return Task.CompletedTask;
    }
}

3. Register the Policy in Program.cs:

builder.Services.AddAuthorization(options =>
{
    options.AddPolicy("VeteranUser", policy =>
        policy.Requirements.Add(new MinimumMembershipRequirement(1)));
});

builder.Services.AddSingleton<IAuthorizationHandler, MinimumMembershipHandler>();

4. Apply the Policy to a Controller:

using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

[ApiController]
[Route("[controller]")]
[Authorize(Policy = "VeteranUser")]
public class SecretDataController : ControllerBase
{
    [HttpGet]
    public IActionResult Get()
    {
        return Ok("This is secret data for veteran users!");
    }
}