I am building a simple “single sign-on” ASP.NET application that interprets the current user’s ASP.NET integrated security credentials to a vendor site’s credentials.  One of the services I wrote required the IIdentity as a constructor parameter to begin the interpretation process. 

This was straightforward with regards to TDD – I simply mocked the IIdentity and kept going.  When I began implementing dependency injection with an IoC container I struggled until I found a nice way to do this with Ninject.

Ninject offers a pretty cool suite of ASP.NET integration points in the Ninject.Framework.Web namespace.  And without using System.Web.Abstractions, the best way I found to resolve a property of HttpContext.Current (User.Identity in my case) was to leverage a provider.

Update (6/25): Duncan Godwin, in the comments, explained what’s perhaps a better way to do this using ToFactoryMethod()

Ninject providers

Ninject providers, IProvider and the simple implementation SimpleProvider<T>, allow the developer to customize the resolution of these hard-to inject objects.  We’re talking providers today on the Ninject list.

Here’s the one I used to resolve IIdentity:

public class WebIdentityProvider : SimpleProvider<IIdentity>
{
    protected override IIdentity CreateInstance(IContext context)
    {
        return HttpContext.Current.User.Identity;
    }

    public override bool IsCompatibleWith(IContext context)
    {
        return HttpContext.Current != null;
    }
}

Here is sample code like I used in Global.asax.cs:

public class Global : NinjectHttpApplication
{
    // ...

    protected override IKernel CreateKernel()
    {
        var module = new InlineModule(
            m => m.Bind<IIdentity>().ToProvider<WebIdentityProvider>(),
            m => m.Bind<IIdentityService>().To<IdentityService>(),
            m => m.Bind<IDisplayName>().To<DisplayName>()
            );
        return new StandardKernel(module, new Log4netModule());
    }
}

When binding to the provider HttpContext.Current and the user’s IIdentity are available.

I have a feeling this isn’t the last one I’ll use.

Here is sample code with log4net’s AspNetTraceAppender turned on (using Ninject logging of course).