Sean Kenny

Custom OWIN IClaimsPrincipal With Ninject

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Having recently started using OWIN to handle authorization, I’ve had to change a few things throughout my web api projects. To have the user’s identity available, I usually create something like:

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public class MyPrincipal : IMyPrincipal
{
    private readonly ClaimsPrincipal claimsPrincipal;

    public MnsPrincipal(ClaimsPrincipal claimsPrincipal)
    {
        this.claimsPrincipal = claimsPrincipal;
    }

    public string Id
    {
        get
        {
            var claim = claimsPrincipal.Claims.FirstOrDefault(c => c.Type == ClaimTypes.NameIdentifier);
            return claim != null ? claim.Value : string.Empty;
        }
    }
}

public interface IMyPrincipal
{
    string Id { get; }
}

This will add the ClaimsPrinciple using composition allowing me to use Ninject like this:

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kernel.Bind<IMyPrincipal>()
    .ToMethod(ctx => new MyPrincipal(HttpContext.Current.GetOwinContext().Authentication.User))
    .InRequestScope();

Now I can get to the logged in user’s Id and claims/roles by using constructor injection:

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public class UsersController : ApiController
{
    private readonly IMyPrincipal myPrinciple;

    public UsersController(IMyPrincipal myPrinciple)
    {
        this.myPrinciple = myPrinciple;
    }

    public HttpResponseMessage Get()
    {
        return Request.CreateResponse(HttpStatusCode.OK, myPrinciple.Id); // will contain my NameIdentifier claim type
    }
}

It also allows me to get to the principal when I am no longer in the web api project. My repository/service/flavour of the month class simply has a contructor with the IMyPrincipal argument.

Previously, using FormsAuth, the principal was available as an IPrincipal using HttpContext.Current.User meaning we could use inheritance. The OWIN approach leads us down the (currently) preferred composition route :–)

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