Необходимо добавить пользовательский заголовок для запроса в unit test

Наконец-то я смог получить HttpContext.Current не null, найдя код в Интернете. Но я все еще не могу добавить пользовательские заголовки к запросу в моем unit test. Вот мой тест:

[TestClass]
public class TagControllerTest
{
    private static Mock<IGenericService<Tag>> Service { get; set; }
    private TagController controller;

    [TestInitialize]
    public void ThingServiceTestSetUp()
    {
        Tag tag = new Tag(1, "people");
        Response<Tag> response = new Response<Tag>();
        response.PayLoad = new List<Tag>() { tag };

        Service = new Mock<IGenericService<Tag>>(MockBehavior.Default);
        Service.Setup(s => s.FindAll("username", "password", "token")).Returns(response);

        controller = new TagController(Service.Object);
        HttpContext.Current = FakeHttpContext();
    }

    public static HttpContext FakeHttpContext()
    {
        var httpRequest = new HttpRequest("", "http://kindermusik/", "");
        var stringWriter = new StringWriter();
        var httpResponce = new HttpResponse(stringWriter);
        var httpContext = new HttpContext(httpRequest, httpResponce);

        var sessionContainer = new HttpSessionStateContainer("id", new SessionStateItemCollection(),
                                                new HttpStaticObjectsCollection(), 10, true,
                                                HttpCookieMode.AutoDetect,
                                                SessionStateMode.InProc, false);

        httpContext.Items["AspSession"] = typeof(HttpSessionState).GetConstructor(
                                    BindingFlags.NonPublic | BindingFlags.Instance,
                                    null, CallingConventions.Standard,
                                    new[] { typeof(HttpSessionStateContainer) },
                                    null)
                            .Invoke(new object[] { sessionContainer });
        httpContext.Request.Headers["username"] = "username"; //It throws a PlatformNotSupportedException exception
        httpContext.Request.Headers["password"] = "password"; //.Headers.Add("blah", "blah") throws same error
        httpContext.Request.Headers["token"] = "token"; //And so to .Headers.Set("blah", "blah")

        return httpContext;
    }

    [TestMethod]
    public void TagControllerGetTest()
    {
        // Arrange
        Response<Tag> result = controller.Get();

        // Assert
        Assert.AreEqual(true, result.IsSuccess);
        Assert.AreEqual(1, result.PayLoad.Count);
        Assert.AreEqual("people", result.PayLoad[0].Name);
    }

Это проверенный код.

public class TagController : ApiController
{
    public IGenericService<Tag> _service;

    public TagController()
    {
        _service = new TagService();
    }

    public TagController(IGenericService<Tag> service)
    {
        this._service = service;
    }

    // GET api/values
    public Response<Tag> Get()
    {
        HttpContext context = HttpContext.Current;
        string username = context.Request.Headers["username"].ToString();
        string password = context.Request.Headers["password"].ToString();
        string token = context.Request.Headers["token"].ToString();
        return (Response<Tag>) _service.FindAll(username, password, token);
    }
}