var container = new UnityContainer();
container.RegisterInstance<IFilterProvider>("FilterProvider", new    FilterProvider(container));
container.RegisterInstance<IActionFilter>("LogActionFilter", new TraceActionFilter());

public class FilterProvider : IFilterProvider
{
    private IUnityContainer container;

    public FilterProvider(IUnityContainer container)
    {
        this.container = container;
    }

    public IEnumerable<Filter> GetFilters(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
    {
        foreach (IActionFilter actionFilter in this.container.ResolveAll<IActionFilter>())
        {
            yield return new Filter(actionFilter, FilterScope.First, null);
        }
    }
}

public class TraceActionFilter : IActionFilter
{
    public void OnActionExecuted(ActionExecutedContext filterContext)
    {
        filterContext.HttpContext.Trace.Write("OnActionExecuted");
        filterContext.HttpContext.Trace.Write("Action " + filterContext.ActionDescriptor.ActionName);
        filterContext.HttpContext.Trace.Write("Controller " + filterContext.ActionDescriptor.ControllerDescriptor.ControllerName);
    }

    public void OnActionExecuting(ActionExecutingContext filterContext)
    {
                filterContext.HttpContext.Trace.Write("OnActionExecuting");
                filterContext.HttpContext.Trace.Write("Action " + filterContext.ActionDescriptor.ActionName);
                filterContext.HttpContext.Trace.Write("Controller " + filterContext.ActionDescriptor.ControllerDescriptor.ControllerName);
    }
}

protected void Application_Start()
    {
        Bootstrapper.Initialise();
        UnityWebApiActivator.Start();
        ConfigureApi(GlobalConfiguration.Configuration); //line added

        AreaRegistration.RegisterAllAreas();
        WebApiConfig.Register(GlobalConfiguration.Configuration);
        FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
        RouteConfig.RegisterRoutes(RouteTable.Routes);
        BundleConfig.RegisterBundles(BundleTable.Bundles);
    }

void ConfigureApi(HttpConfiguration config)
    {
        var unity = new UnityContainer();
        unity.RegisterType<ProductsApiController>();
        unity.RegisterType<CategoriesApiController>();

        unity.RegisterType<IProductService, ProductService>(
            new HierarchicalLifetimeManager());
        unity.RegisterType<IProductsDatabase, ProductsDatabase>(
             new HierarchicalLifetimeManager());

        unity.RegisterType<ICategorieService, CategorieService>(
            new HierarchicalLifetimeManager());
        unity.RegisterType<ICategoriesDatabase, CategoriesDatabase>(
             new HierarchicalLifetimeManager());

        unity.RegisterType<ILogProvider, ElmahProvider>(
             new HierarchicalLifetimeManager());

        unity.RegisterType<IRootController, RootController>(
            new HierarchicalLifetimeManager());

        config.DependencyResolver = new IoCContainer(unity);

        //ADDED PARTS
        var providers = GlobalConfiguration.Configuration.Services.GetFilterProviders().ToList();
        config.Services.Add(
            typeof(System.Web.Http.Filters.IFilterProvider),
            new Filter2Provider(UnityConfig.GetConfiguredContainer()));

        var defaultprovider = providers.First(p => p is System.Web.Http.Filters.ActionDescriptorFilterProvider);
        config.Services.Remove(typeof(System.Web.Http.Filters.IFilterProvider), defaultprovider);
    }

public class UnityActionFilterProvider
    : System.Web.Http.Filters.ActionDescriptorFilterProvider,
      System.Web.Http.Filters.IFilterProvider
{
    private readonly IUnityContainer container;

    public UnityActionFilterProvider(IUnityContainer container)
    {
        this.container = container;
    }

    public new IEnumerable<FilterInfo> GetFilters(HttpConfiguration configuration,
        HttpActionDescriptor actionDescriptor)
    {
        foreach (IActionFilter actionFilter in container.ResolveAll<IActionFilter>())
        {
            // TODO: Determine correct FilterScope
            yield return new FilterInfo(actionFilter, FilterScope.Global);
        }
    }
}

var providers =
    GlobalConfiguration.Configuration.Services.GetFilterProviders().ToList();

GlobalConfiguration.Configuration.Services.Add(
    typeof(System.Web.Http.Filters.IFilterProvider),
    new UnityActionFilterProvider(UnityConfig.GetConfiguredContainer()));

var defaultprovider = providers.First(p => p is ActionDescriptorFilterProvider);

GlobalConfiguration.Configuration.Services.Remove(
    typeof(System.Web.Http.Filters.IFilterProvider),
    defaultprovider);