Authentication with Microsoft.Owin.Testing.TestSer

I've just moved to using OWIN\Katana for a web api project. It uses Windows Authentication. This seems to be working, but most of my integration tests have broken. They were previously just using an In-Memory HttpServer but I've changed to using Microsoft.Owin.Testing.TestServer. I've replaced something like this in my test setup:

        var config = new HttpConfiguration { IncludeErrorDetailPolicy = IncludeErrorDetailPolicy.Always };
        config.EnableQuerySupport();
        Server = new HttpServer(config);
        MyConfigClass.Configure(config);
        WebApiConfig.Register(config);

with a simpler:

TestServer = TestServer.Create<Startup>();

But whereas previously I could just put the following to "fake" authentication with the in-memory server:

Thread.CurrentPrincipal = new ClientRolePrincipal(new HttpListenerBasicIdentity(Username, Password));

This now doesn't work. I get the following for all requests:

System.Exception : {"Message":"Authorization has been denied for this request."}

How do I Authenticate with the In-Memory OWIN test server or at least by-pass the authentication?

I've been able to workaround this in a way that I'm sure is sub-optimal, but will have to do until I come across a better solution or one of you fine folk tells me a better way to do this :) I've done it as follows:

In my Startup class I've added a CreateAuthFilter hook which we'll see later is used only in integration tests:

// Sample Startup class
public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        var config = new HttpConfiguration();

        // Use CreateFilter Method to create Authorisation Filter -  if not null add it
        var authFilter = CreateAuthFilter();
        if(authFilter != null)
            config.Filters.Add(authFilter);

        // Other configuration and middleware...
    }

    public static Func<IFilter> CreateAuthFilter = () => null;
}

Implemented an Authorization Filter which will only be used in Integration Tests:

public class TestAuthFilter : IAuthenticationFilter
{
    static TestAuthFilter()
    {
        TestUserId = "TestDomain\\TestUser";
    }

    public bool AllowMultiple { get; private set; }

    public async Task AuthenticateAsync(HttpAuthenticationContext context, CancellationToken cancellationToken)
    {
        context.Principal = new ClientRolePrincipal(new HttpListenerBasicIdentity(TestUserId, "password")); ;
    }

    public static string TestUserId { get; set; }

    public async Task ChallengeAsync(HttpAuthenticationChallengeContext context, CancellationToken cancellationToken)
    {

    }
}

In the SetUp code for my Integration Tests I inject the Test Authorization Filter:

Startup.CreateAuthFilter = () => new TestAuthFilter();
var TestServer = TestServer.Create<Startup>();

When needed in specific tests, I set the TestUserId to a known value, and other tests just seem to work because the Auth Filter is present:
```
TestAuthFilter.TestUserId = testUser.UserId;
```

I'm sharing this here incase it helps others out there, but please someone tell me a better way! At the very least I'm sure there's a better way to inject my Test Filter without including code in Startup... I just haven't thought of it.