Using Claims Transformation with Windows Authentication

Question

Using Windows Authentication in an ASP.NET Core 2.1 application. In the database we have a User table that stores users along with their Sid. It has a 1-1 relationship with UserProfile which has information I want to use for Claims.

I added a this service for Claims Transformation:

public class UserStatusClaimsTransformation : IClaimsTransformation
{
    private readonly MyDbContext _context;

    public UserStatusClaimsTransformation(MyDbContext context)
    {
        _context = context;
    }

    public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
    {
        if (principal.Identity is WindowsIdentity identity)
        {
            User user = await _context.User
                .Include(u => u.UserProfile)
                .Where(u => new SecurityIdentifier(u.WindowsSid, 0) == identity.User)
                .SingleOrDefaultAsync();

            if (user != null)
            {
                identity.AddClaim(new Claim("Status", user.UserProfile));
            }
        }

        return principal;
    }
}

My issue is, once this service is registered, the IPrincipal accessed elsewhere in the pipeline is now a ClaimsPrincipal instead of a WindowsPrincipal. Example, in MyDbContext I inject IPrincipal via DI:

public MyDbContext(DbContextOptions<MyDbContext> options, IPrincipal principal) : base(options)
{
    _principal = principal;
}

Previously, this was a WindowsPrincipal and I could get the Username from _principal.Identity.Name, but after registering my Claims Transformer it is a ClaimsPrincipal and _principal.Identity.Name is null. Is there a way to keep the IPrincipal provided through DI as a WindowsPrincipal after using the Claims Transformation?

Polina · Accepted Answer · 2019-05-23 14:46:01Z

I use ASP.NET MVC Core 2.2, and it's probably too late for you, but maybe it would be helpful for someone else. Then I started my application I didn't find helpful information, and it was my custom suggestion. It works, you can use it:

 public class ClaimsLoader : IClaimsTransformation
{        
    private IUserrolesRepository repository;
    public ClaimsLoader(IUserrolesRepository repo)
    {
        repository = repo;
    }
    public bool ifRoleExist(ClaimsPrincipal principal, string value)
    {
        var ci = (ClaimsIdentity)principal.Identity;
        var claim = principal.FindAll(ci.RoleClaimType);
        foreach (var c in claim)
        {
            if (c.Value == value)
                return true;
        }
        return false;
    }

    public async Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
   {            
        var ci = (ClaimsIdentity)principal.Identity;
        List<Userrole> userroles = await repository.Userroles.Include(u => u.R).Include(u => u.U).Where(u => u.U.Uid==principal.Identity.Name.Substring(10)).ToListAsync();

        if (userroles!=null)                {

            foreach (Userrole ur in userroles)
            {
                Claim claim = new Claim(ci.RoleClaimType, ur.Rid); 
                if (!ifRoleExist(principal, ur.Rid))                  
                ci.AddClaim(claim);
            }
        }                     
        return await Task.FromResult(principal);   
    }
}

I didn't use ApplicationDbContext here, instead I use repository, this is repository interface:

    public interface IUserrolesRepository
{
    IQueryable<Userrole> Userroles { get; }

}

and EFUserRepository class:

public class EFUserrolesRepository : IUserrolesRepository
{
    private ApplicationDbContext context;

    public EFUserrolesRepository(ApplicationDbContext ctx)
    {
        context = ctx;
    }

    public IQueryable<Userrole> Userroles => context.Userrole;

}

this is my Userrole class (just in case if someone need it):

public partial class Userrole
{
    public string Rid { get; set; }//pk
    public string Uid { get; set; }//pk

    public virtual Role R { get; set; }//fk
    public virtual User U { get; set; }//fk
}

In ApplicationDbContext I did some changes too:

public class ApplicationDbContextFactory
       : IDesignTimeDbContextFactory<ApplicationDbContext>
{

    public ApplicationDbContext CreateDbContext(string[] args) =>
        Program.BuildWebHost(args).Services
            .GetRequiredService<ApplicationDbContext>();
}

and finally in Startup:

        services.AddSingleton<IClaimsTransformation, ClaimsLoader>();
        services.AddTransient<IUserrolesRepository, EFUserrolesRepository>();
        services.AddMvc();
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);



services.AddAuthentication(Microsoft.AspNetCore.Server.IISIntegration.IISDefaults.AuthenticationScheme);

and Program.cs file changed too:

public class Program
{
    public static void Main(string[] args)
    {
        //CreateWebHostBuilder(args).Build().Run();
        BuildWebHost(args).Run();
    }

    /*public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();*/

    public static IWebHost BuildWebHost(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>()
            .UseDefaultServiceProvider(options =>
                options.ValidateScopes = false)
            .Build();
}

That's it. It should work.

Upvoted. Pretty good and detailed answer! Hey @valuator This deserves settings this should be The Answer :).

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