Inject IOwinContext with Web API and Ninject

Question

Using Web API 2 and OWIN hosting with Ninject.

I would like to inject the current IOwinContext into certain services (so I can get at the Request to get the principal to do some data filtering).

With Web Hosting I would, in the old days, simply have used HttpContext.Current but that is not an option with OWIN hosting (and good riddance).

This SO question explains how to do it with Autofac. Essentially, you create a Dependency Scope and then, on each request, calls Autofac's Registerinstance to register the current IOwinContext into that dependency scope like so:

app.Use(async (ctx, next) =>
{
    // this creates a per-request, disposable scope
    using (var scope = container.BeginLifetimeScope(b =>
    {
        // this makes owin context resolvable in the scope
        b.RegisterInstance(ctx).As<IOwinContext>();
    }))
    {
        // this makes scope available for downstream frameworks
        ctx.Set<ILifetimeScope>("idsrv:AutofacScope", scope);
        await next();
    }
}); 

That is very elegant. With Ninject and the Ninject.Web.WebApi.OwinHosting I already get a named scope for each request so that plumbing is taken care of. However, I haven't been able to find any way in ninject to mirror AutoFac's RegisterInstance method: The key here is that this binding is only valid within this particular dependency scope.

I have read up on the various options around Scope but everything I have found relies on being able to declare constants or ToMethod. What I am looking to do here is to say, "okay, I now have a ninject dependency scope and if anyone asks for an IOwinContext from this scope, give them this instance that I already have.

Note

I do understand that I can get the current context from within my controller and pass it on, but that rather defeats the purpose of what I am trying to do; I want my DbContext to understand who the user is so it can filter the data. And, of course, once I can get the IOwinContext I won't actually pass that to the DbContext, rather I will use a ToMethod or similar to extract the ClaimsPrincipal but that is out of scope of this question.

Answer 1

DISCLAIMER: This is a hack. It works, but it feels very unclean. Use at your peril.

In essence, you can create an OwinContextHolder class, bind it InRequestScope and use a DelegatingHandler to populate it on each request. Something like this:

public class OwinContextHolder
{
    public IOwinContext OwinContext { get; set; }
}

public class OwinContextHolderModule : NinjectModule
{
    public override void Load()
    {
        // Instead of a NinjectModule you can of course just register the service
        this.Kernel.Bind<OwinContextHolder>().ToSelf().InRequestScope();
    }
}

Your delegating handler:

public class SetOwinContextHandler : DelegatingHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var holder = request.GetDependencyScope().GetService(typeof(OwinContextHolder)) as OwinContextHolder;
        if (holder != null)
        {
            holder.OwinContext = request.GetOwinContext();
        }
        return base.SendAsync(request, cancellationToken);
    }
}

Finally add the DelegatingHandler to your Startup class:

public void Configuration(IAppBuilder app)
{
    var webApiConfiguration = new HttpConfiguration();
    webApiConfiguration.Routes.MapHttpRoute(...);

    webApiConfiguration.MessageHandlers.Add(new SetOwinContextHandler());

    app.UseNinjectMiddleware(CreateKernel);
    app.UseNinjectWebApi(webApiConfiguration);
}

You can now inject OwinContextHolder into your classes.

Note that if you have your API in a separate assembly from your host, you may have problems with InRequestScope silently not working (as in, you get a different object every time you request one and no errors). If you do, see https://groups.google.com/forum/#!topic/ninject/Wmy83BhhFz8.