ASP.NET Core - Authorization Using Windows Authentication

Question

I have configured my web api to work with windows authentication. My goal is essentially to restrict certain actions in my controllers based on a users windows account. Some will be able to preform read actions while others will be able to preform actions that will write to the underlying database. I have found plenty of documentation on how to set up claims based authorization which is the route I think I need to go. What I have not found is how to set this up with windows auth. I think I am missing a middle step such as registering the windows auth as the identity provider?

startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();

    services.AddAuthentication(IISDefaults.AuthenticationScheme);

    services.AddAuthorization(options =>
    {
        options.AddPolicy("readOnly", policy =>
                          policy.RequireClaim(`???????????????????????`));
        options.AddPolicy("write", policy =>
                          policy.RequireClaim(`???????????????????????`));
    });
}

Controller

[Authorize(Policy = "ReadOnly")]
public class MyController : Controller
{
    public ActionResult SomeReadOnlyAction()
    {
        //Return data from database
    }

    [Authorize(Policy = "Write")]
    public ActionResult AWriteAction()
    {
        //Create/Update/Delete data from database
    }
}

I guess another way to ask this question is how do you configure or access claims/roles etc... with windows authentication.

Solution

That seems you want to use claims-based authorization via policies . After setting windows authentication in your application , you could add custom claim to ClaimsPrincipal ,check user's identity and confirm which permission current user has :

1. You can add a claims transformation service to your application:

   class ClaimsTransformer : IClaimsTransformation
   {
       public Task<ClaimsPrincipal> TransformAsync(ClaimsPrincipal principal)
       {
           var id = ((ClaimsIdentity)principal.Identity);
   
           var ci = new ClaimsIdentity(id.Claims, id.AuthenticationType, id.NameClaimType, id.RoleClaimType);
           if (ci.Name.Equals("name"))
           {
               ci.AddClaim(new Claim("permission", "readOnly"));
           }
           else
           {
               ci.AddClaim(new Claim("permission", "write"));
   
           }
   
   
           var cp = new ClaimsPrincipal(ci);
   
           return Task.FromResult(cp);
       }
   }
   

2. Add to Startup.cs(.net Core 2.0) :

       services.AddTransient<IClaimsTransformation, ClaimsTransformer>();
   

3. Set your policy :

       services.AddAuthorization(options =>
       {
           options.AddPolicy("Readonly", policy =>
                             policy.RequireClaim("permission", "readOnly"));
   
           options.AddPolicy("Write", policy =>
                           policy.RequireClaim("permission", "write"));
       });
   

4. Restrict access to a controller or action by requiring this policy:

       [Authorize(Policy = "Write")]
       public IActionResult Contact()
       {
           ViewData["Message"] = "Your contact page.";
   
           return View();
       }
   

If you have already add groups(write,readonly) in your AD and add the related users to group , you can also check the groups :

public static class Security
{
    public static bool IsInGroup(this ClaimsPrincipal User, string GroupName)
    {
        var groups = new List<string>();

        var wi = (WindowsIdentity)User.Identity;
        if (wi.Groups != null)
        {
            foreach (var group in wi.Groups)
            {
                try
                {
                    groups.Add(group.Translate(typeof(NTAccount)).ToString());
                }
                catch (Exception)
                {
                    // ignored
                }
            }
            return groups.Contains(GroupName);
        }
        return false;
    }
}

And use like :

 if (User.IsInGroup("GroupName"))
 {

 }

Comments

[LCaraway]

This is great! Where does the if(User.IsInGroup)... go? Does it get dropped in the ClaimsTransformer Class?

[LCaraway]

Or would you use that as an alternative to the ClaimsTransformer?

[Nan Yu]

@LCaraway , it depends you , it can be in any class .

[LCaraway]

When the group.Translate() is ran it returns an exception stating the trust relationship between the workstation and the primary domain has failed...

[Nan Yu]

See how to solve the issue :support.microsoft.com/en-hk/help/2771040/… and support.citrix.com/article/CTX227147

[Stef Chäser]

Isn't the code faster if you translate the AD-GroupName to the SID representation. IdentityReference sidAdGroup = new NTAccount(GroupName).Translate(typeof(SecurityIdentifier)); then comparing it with the SIDs in wi.Groups (Instead of translate/cast all wi.Groups to NTAccount?)

[Caesar Tex]

Why not just use the built in User.IsInRole(AD Group Name) for option 2?

[jondow]

Great answer, really helpful thanks