In this blog post, I’ll explore advanced techniques to secure your Minimal APIs in .NET 8. Security is critical for any API, and with the rise of Minimal APIs, it’s essential to understand how to protect them effectively. We’ll dive into JWT authentication, OAuth2, and custom authorization policies.

Why Security in Minimal APIs?

Minimal APIs are streamlined, but they still require the same level of security as any other API architecture. The challenge lies in ensuring that the simplicity of Minimal APIs doesn't compromise their security.

1. Implementing JWT Authentication in Minimal APIs

JSON Web Tokens (JWT) are a popular way to secure APIs due to their stateless nature and the ease of validating tokens. Here’s how to integrate JWT authentication into your .NET 8 Minimal API:

// Add JWT Authentication in Program.cs
var builder = WebApplication.CreateBuilder(args);
builder.Services.AddAuthentication("Bearer")
    .AddJwtBearer(options =>
    {
        options.Authority = "https://your-auth-server.com";
        options.Audience = "your-api";
    });

Now, secure an endpoint by adding [Authorize] attribute:

var app = builder.Build();
app.MapGet("/secure-endpoint", [Authorize] () => "This is a secure endpoint")
    .RequireAuthorization();

2. OAuth2 Integration for Third-Party Authentication

OAuth2 is widely used to allow third-party authentication from providers like Google, Facebook, or GitHub. In .NET 8, you can easily integrate it using libraries like Microsoft.AspNetCore.Authentication.OAuth:

builder.Services.AddAuthentication()
    .AddGoogle(options =>
    {
        options.ClientId = "your-client-id";
        options.ClientSecret = "your-client-secret";
    });

Now users can authenticate using their Google account, providing seamless integration with your Minimal API.

3. Custom Authorization Policies

For more granular control, custom authorization policies let you define access rules beyond just roles or claims:

builder.Services.AddAuthorization(options =>
{
    options.AddPolicy("AdminOnly", policy => policy.RequireClaim("role", "admin"));
});

app.MapGet("/admin", [Authorize(Policy = "AdminOnly")] () => "Admin Content");

This ensures only users with a specific role or claim can access the /admin route.

4. Rate Limiting and IP Restriction

To prevent abuse, rate limiting can be a great tool. You can also restrict access to specific IP addresses:

app.Use(async (context, next) =>
{
    var ip = context.Connection.RemoteIpAddress;
    if (ip != null && ip.ToString() == "123.456.789.0")
    {
        await context.Response.WriteAsync("Access Denied");
    }
    else
    {
        await next();
    }
});

Conclusion

Securing Minimal APIs in .NET 8 doesn’t have to be complex. With JWT, OAuth2, and custom authorization policies, you can implement robust security mechanisms to protect your API while maintaining its simplicity. Remember to layer your security with techniques like rate limiting and IP restrictions to prevent abuse.