Fga.Net.DependencyInjection 0.6.0-alpha

OpenFGA & Auth0 FGA for ASP.NET Core + Worker Services

Note: This project is in its early stages and will have breaking changes as FGA matures.

Packages

Fga.Net.DependencyInjection: Provides dependency injection/configuration extensions for OpenFga.Sdk

Fga.Net.AspNetCore: Additionally includes Authorization middleware to support FGA checks as part of a request's lifecycle.

Getting Started

This package is compatible with the OSS OpenFGA as well as the managed Auth0 FGA service.

Please ensure you have a basic understanding of how FGA works before continuing: OpenFGA Docs or Auth0 FGA Docs

ASP.NET Core Setup

This tutorial assumes you have authentication setup within your project, such as JWT bearer authentication via Auth0.

Install Fga.Net.AspNetCore from Nuget before continuing.

Auth0 FGA

Ensure you have a Store ID, Client ID, and Client Secret ready from How to get your API keys.

1. Add your StoreId, ClientId and ClientSecret to your application configuration, ideally via the dotnet secrets manager.
2. Add the following code to your ASP.NET Core services configuration:

builder.Services.AddOpenFga(x =>
{
    x.WithAuth0FgaDefaults(builder.Configuration["Auth0Fga:ClientId"], builder.Configuration["Auth0Fga:ClientSecret"]);

    x.StoreId = builder.Configuration["Auth0Fga:StoreId"];
});

The WithAuth0FgaDefaults extension will configure the relevant OpenFGA client settings to work with Auth0 FGA's US environment.

OpenFGA

OpenFGA configuration is very similar to the SDK Setup Guide

1. Add the FGA ApiScheme, ApiHost & StoreId to your application configuration.
2. Add the following code to your ASP.NET Core configuration:

builder.Services.AddOpenFga(x =>
{
    x.ApiScheme = builder.Configuration["Fga:ApiScheme"];
    x.ApiHost = builder.Configuration["Fga:ApiHost"];
    x.StoreId = builder.Configuration["Fga:StoreId"];
});

Authorization Policy Setup

Now we'll need to setup our authorization middleware like so:

// Register the authorization policy
builder.Services.AddAuthorization(options =>
{
    options.AddPolicy(FgaAuthorizationDefaults.PolicyKey, 
        p => p
            .RequireAuthenticatedUser()
            .AddFgaRequirement());
});

Next, create an attribute that inherits from TupleCheckAttribute. From here, you can pull the metadata you require to perform your tuple checks out of the HTTP request. For example, an equivalent to the How To Integrate Within A Framework example would be:

public class EntityAuthorizationAttribute : TupleCheckAttribute
{
    private readonly string _prefix;
    private readonly string _routeValue;
    public EntityAuthorizationAttribute(string prefix, string routeValue)
    {
        _prefix = prefix;
        _routeValue = routeValue;
    }

    public override ValueTask<string> GetUser(HttpContext context) 
        => ValueTask.FromResult(context.User.Identity!.Name!);

    public override ValueTask<string> GetRelation(HttpContext context) 
        => ValueTask.FromResult(context.Request.Method switch 
        {
            "GET" => "viewer",
            "POST" => "writer",
            _ => "owner"
        });

    public override ValueTask<string> GetObject(HttpContext context) 
        => ValueTask.FromResult($"{_prefix}:{context.GetRouteValue(_routeValue)}");
}

Now apply the Authorize and EntityAuthorization attributes to your controller(s):

    // Traditional Controllers
    [ApiController]
    [Route("[controller]")]
    [Authorize(FgaAuthorizationDefaults.PolicyKey)]
    public class DocumentController : ControllerBase
    {  
        [HttpGet("view/{documentId}")]
        [EntityAuthorization("doc", "documentId")]
        public string GetByConvention(string documentId)
        {
            return documentId;
        }
    }

    // Minimal APIs
    app.MapGet("/viewminimal/{documentId}", (string documentId) => Task.FromResult(documentId))
        .RequireAuthorization(FgaAuthorizationDefaults.PolicyKey)
        .WithMetadata(new EntityAuthorizationAttribute("doc", "documentId"));

If you need to manually perform checks, inject the Auth0FgaApi as required.

An additional pre-made attribute that allows all tuple values to be hardcoded strings ships with the package (StringTupleCheckAttribute). This attribute is useful for testing and debug purposes, but should not be used in a real application.

Worker Service / Generic Host Setup

Fga.Net.DependencyInjection ships with the AddOpenFgaClient service collection extension that handles all required wire-up.

To get started:

1. Install Fga.Net.DependencyInjection
2. Add your StoreId, ClientId and ClientSecret Auth0 FGA configuration OR ApiScheme, ApiHost & StoreId OpenFGA configuration to your application configuration, ideally via the dotnet secrets manager.
3. Register the authorization client:

var host = Host.CreateDefaultBuilder(args)
    .ConfigureServices((context, services) =>
    {
        services.AddOpenFgaClient(config =>
        {
            // Auth0 FGA
            config.WithAuth0FgaDefaults(context.Configuration["Auth0Fga:ClientId"], context.Configuration["Auth0Fga:ClientSecret"]);
            config.StoreId = context.Configuration["Auth0Fga:StoreId"];

            // OpenFGA
            config.ApiScheme = context.Configuration["Fga:ApiScheme"];
            config.ApiHost = context.Configuration["Fga:ApiHost"];
            config.StoreId = context.Configuration["Fga:StoreId"];
        });

        services.AddHostedService<MyBackgroundWorker>();
    })
    .Build();

await host.RunAsync();

4. Request the client in your services:

public class MyBackgroundWorker : BackgroundService
{
    private readonly Auth0FgaApi _authorizationClient;

    public MyBackgroundWorker(Auth0FgaApi authorizationClient)
    {
        _authorizationClient = authorizationClient;
    }

    protected override Task ExecuteAsync(CancellationToken stoppingToken)
    {
        // Do work with the client
    }
}

Standalone client setup

See the OpenFGA.Sdk docs

Disclaimer

I am not affiliated with nor represent Auth0 or OpenFGA. All support queries regarding the underlying service should go to the Auth0 Labs Discord.