Integration testing with in-memory IdentityServer

I understand there is a need for a more complete answer than what @james-fera posted. I have learned from his answer and made a github project consisting of a test project and API project. The code should be self-explanatory and not hard to understand.

https://github.com/emedbo/identityserver-test-template

The IdentityServerSetup.cs class https://github.com/emedbo/identityserver-test-template/blob/master/tests/API.Tests/Config/IdentityServerSetup.cs can be abstracted away e.g. NuGetted away, leaving the base class IntegrationTestBase.cs

The essences is that can make the test IdentityServer work just like a normal IdentityServer, with users, clients, scopes, passwords etc. I have made the DELETE method [Authorize(Role="admin)] to prove this.

Instead of posting code here, I recommend read @james-fera's post to get the basics then pull my project and run tests.

IdentityServer is such a great tool, and with the ability to use the TestServer framework it gets even better.

You were on the right track with the code posted in your initial question.

The IdentityServerAuthenticationOptions object has properties to override the default HttpMessageHandlers it uses for back channel communication.

Once you combine this with the CreateHandler() method on your TestServer object you get:

//build identity server here

var idBuilder = new WebBuilderHost();
idBuilder.UseStartup<Startup>();
//...

TestServer identityTestServer = new TestServer(idBuilder);

var identityServerClient = identityTestServer.CreateClient();

var token = //use identityServerClient to get Token from IdentityServer

//build Api TestServer
var options = new IdentityServerAuthenticationOptions()
{
    Authority = "http://localhost:5001",

    // IMPORTANT PART HERE
    JwtBackChannelHandler = identityTestServer.CreateHandler(),
    IntrospectionDiscoveryHandler = identityTestServer.CreateHandler(),
    IntrospectionBackChannelHandler = identityTestServer.CreateHandler()
};

var apiBuilder = new WebHostBuilder();

apiBuilder.ConfigureServices(c => c.AddSingleton(options));
//build api server here

var apiClient = new TestServer(apiBuilder).CreateClient();
apiClient.SetBearerToken(token);

//proceed with auth testing

This allows the AccessTokenValidation middleware in your Api project to communicate directly with your In-Memory IdentityServer without the need to jump through hoops.

As a side note, for an Api project, I find it useful to add IdentityServerAuthenticationOptions to the services collection in Startup.cs using TryAddSingleton instead of creating it inline:

public void ConfigureServices(IServiceCollection services)
{
    services.TryAddSingleton(new IdentityServerAuthenticationOptions
    {
        Authority = Configuration.IdentityServerAuthority(),
        ScopeName = "api1",
        ScopeSecret = "secret",
        //...,
    });
}

public void Configure(IApplicationBuilder app)
{
    var options = app.ApplicationServices.GetService<IdentityServerAuthenticationOptions>()

    app.UseIdentityServerAuthentication(options);

    //...
}

This allows you to register the IdentityServerAuthenticationOptions object in your tests without having to alter the code in the Api project.

I think you probably need to make a test double fake for your authorization middleware depending on how much functionality you want. So basically you want a middleware that does everything that the Authorization middleware does minus the back channel call to the discovery doc.

IdentityServer4.AccessTokenValidation is a wrapper around two middlewares. The JwtBearerAuthentication middleware, and the OAuth2IntrospectionAuthentication middleware. Both of these grab the discovery document over http to use for token validation. Which is a problem if you want to do an in-memory self-contained test.

If you want to go through the trouble you will probably need to make a fake version of app.UseIdentityServerAuthentication that doesnt do the external call that fetches the discovery document. It only populates the HttpContext principal so that your [Authorize] policies can be tested.

Check out how the meat of IdentityServer4.AccessTokenValidation looks here. And follow up with a look at how JwtBearer Middleware looks here

We stepped away from trying to host a mock IdentityServer and used dummy/mock authorizers as suggested by others here.

Here's how we did that in case it's useful:

Created a function which takes a type, creates a test Authentication Middleware and adds it to the DI engine using ConfigureTestServices (so that it's called after the call to Startup.)

internal HttpClient GetImpersonatedClient<T>() where T : AuthenticationHandler<AuthenticationSchemeOptions>
    {
        var _apiFactory = new WebApplicationFactory<Startup>();

        var client = _apiFactory
            .WithWebHostBuilder(builder =>
            {
                builder.ConfigureTestServices(services =>
                {
                    services.AddAuthentication("Test")
                        .AddScheme<AuthenticationSchemeOptions, T>("Test", options => { });
                });
            })
            .CreateClient(new WebApplicationFactoryClientOptions
            {
                AllowAutoRedirect = false,
            });

        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Test");

        return client;
    }

Then we create what we called 'Impersonators' (AuthenticationHandlers) with the desired roles to mimic users with roles (We actually used this as a base class, and create derived classes based on this to mock different users):

public abstract class FreeUserImpersonator : AuthenticationHandler<AuthenticationSchemeOptions>
{
    public Impersonator(
        IOptionsMonitor<AuthenticationSchemeOptions> options,
        ILoggerFactory logger, UrlEncoder encoder, ISystemClock clock)
        : base(options, logger, encoder, clock)
    {
        base.claims.Add(new Claim(ClaimTypes.Role, "FreeUser"));
    }

    protected List<Claim> claims = new List<Claim>();

    protected override Task<AuthenticateResult> HandleAuthenticateAsync()
    {
        var identity = new ClaimsIdentity(claims, "Test");
        var principal = new ClaimsPrincipal(identity);
        var ticket = new AuthenticationTicket(principal, "Test");

        var result = AuthenticateResult.Success(ticket);

        return Task.FromResult(result);
    }
}

Finally, we can perform our integration tests as follows:

// Arrange
HttpClient client = GetImpersonatedClient<FreeUserImpersonator>();

// Act
var response = await client.GetAsync("api/things");

// Assert
Assert.That.IsSuccessful(response);