Authorization Filter Dependency Injection with ASP.New MVC 4 Web Api

Question

I'm trying to implement dependency injection on a MVC 4 Web Api Authorization Filter. I created a FilterProvider that inherits from ActionDescriptorFilterProvider:

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

    public UnityWebApiFilterAttributeFilterProvider(IUnityContainer container)
    {
        _container = container;
    }

    public IEnumerable<FilterInfo> GetFilters(HttpConfiguration configuration, HttpActionDescriptor actionDescriptor)
    {
        var filters = base.GetFilters(configuration, actionDescriptor);

        this.BuildUpAttributes(filters);

        return filters;
    }

    private void BuildUpAttributes(IEnumerable filterInfo)
    {
        foreach (FilterInfo filter in filterInfo)
        {
            object o = _container.BuildUp(filter.GetType(), filter);
        }
    }
}

and I set this provider to be the default provider in my Global.asax file:

var providers = GlobalConfiguration.Configuration.Services.GetFilterProviders().ToList();
        //Remove the default provider
        var defaultprovider = providers.Single(i => i is ActionDescriptorFilterProvider);
        GlobalConfiguration.Configuration.Services.Remove(typeof(System.Web.Http.Filters.IFilterProvider), defaultprovider);
        //Add our custom provider
        GlobalConfiguration.Configuration.Services.Add(typeof(System.Web.Http.Filters.IFilterProvider), new UnityWebApiFilterAttributeFilterProvider(new UnityContainer()));

I also added a dependency in the AuthorizationFilter:

public class WebApplicationApiAuthorizeAttribute : System.Web.Http.AuthorizeAttribute
{

    [Dependency]
    public IAuthorizationHelper AuthorizationHelper { get; set; }

    #region OnAuthorization
    public override void OnAuthorization(System.Web.Http.Controllers.HttpActionContext actionContext)
{
    //Authorization code, which uses the AuthorizationHelper lives here
}   

}

and I set up a mapping in my Unity configuration file:

container.RegisterType<WebApplicationApiAuthorizeAttribute>(new InjectionMember[]
            {
                new InjectionProperty("AuthorizationHelper", new ResolvedParameter<IAuthorizationHelper>())
            });

        container.RegisterType<IAuthorizationHelper, WebAuthorizationHelper>(new InjectionMember[]
            {
                new InjectionProperty("Cache", new ResolvedParameter<ICache>(cacheType)),
                new InjectionProperty("UserSessionManager", new ResolvedParameter<IUserSessionManager>()),
                new InjectionProperty("AuthorizationPermissionManager", new ResolvedParameter<IAuthorizationPermissionManager>()),
                new InjectionProperty("ExceptionLogger", new ResolvedParameter<IExceptionLogger>()),
            });

I can see that the "BuildUpAttributes" method in the UnityWebApiFilterAttributeFilterProvider class is executed and that the filter is passed into the _container.BuildUp(...) method, however, the "IAuthorizationHelper" dependency in the WebApplicationApiAuthorizeAttribute does not get resolved. It is null, when I debug the WebApplicationApiAuthorizeAttribute.

So why is this dependency not being resolved?

Answer 1

There are two errors in your code.

1. You're building up the FilterInfo object instead of its Instance:

   foreach (FilterInfo filter in filterInfo)
   {
       object o = _container.BuildUp(filter.GetType(), filter);
   }
   

   But this is the correct code:

   foreach (FilterInfo filter in filterInfo)
   {
       _container.BuildUp(filter.Instance.GetType(), filter.Instance);
   }
   

2. Your custom UnityWebApiFilterAttributeFilterProvider gets a new and empty container:

   GlobalConfiguration.Configuration.Services.Add(
       typeof(System.Web.Http.Filters.IFilterProvider), 
       new UnityWebApiFilterAttributeFilterProvider(new UnityContainer()));
   

   But you should pass on the application's configured container:

   GlobalConfiguration.Configuration.Services.Add(
       typeof(System.Web.Http.Filters.IFilterProvider), 
       new UnityWebApiFilterAttributeFilterProvider(container));