User.Identity fluctuates between ClaimsIdentity and WindowsIdentity

Question

I have an MVC site that allows logging in using both Forms login and Windows Authentication. I use a custom MembershipProvider that authenticated the users against Active Directory, the System.Web.Helpers AntiForgery class for CSRF protection, and Owin cookie authentication middle-ware.

During login, once a user has passed authentication against Active Directory, I do the following:

IAuthenticationManager authenticationManager = HttpContext.Current.GetOwinContext().Authentication;
authenticationManager.SignOut(StringConstants.ApplicationCookie);
var identity = new ClaimsIdentity(StringConstants.ApplicationCookie,
    ClaimsIdentity.DefaultNameClaimType,
    ClaimsIdentity.DefaultRoleClaimType);
if(HttpContext.Current.User.Identity is WindowsIdentity)
{
    identity.AddClaims(((WindowsIdentity)HttpContext.Current.User.Identity).Claims);
}
else
{
    identity.AddClaim(new Claim(ClaimTypes.Name, userData.Name));
}
identity.AddClaim(new Claim("http://schemas.microsoft.com/accesscontrolservice/2010/07/claims/identityprovider", "Active Directory"));
identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, userData.userGuid));
authenticationManager.SignIn(new AuthenticationProperties() { IsPersistent = false }, identity);

My SignOut function looks like this:

IAuthenticationManager authenticationManager = HttpContext.Current.GetOwinContext().Authentication;
authenticationManager.SignOut(StringConstants.ApplicationCookie);

Logging in is performed via a jQuery.ajax request. On success, the Window.location is updated to the site's main page.

Logging in with both Forms and IntegratedWindowsAuthentication (IWA) works, but I've run into a problem when logging in with IWA. This is what happens:

1. The user selects IWA on the login page and hits the submit button. This is sent to the regular login action via an ajax request.
2. The site receives the request, sees the "use IWA" option and redirects to the relevant action. 302 response is sent.
3. The browser automatically handles the 302 response and calls the redirect target.
4. A filter sees that the request is headed to the IWA login action and that User.Identity.IsAuthenticated == false. 401 response is sent.
5. The browser automatically handles the 401 response. If the user has not authenticated using IWA in the browser yet, they get a popup to do so (default browser behavior). Once credentials have been received, the browser performs the same request with user credentials.
6. The site receives the authenticated request and impersonates the user to perform a check against Active Directory. If the user passes authentication, we finalize SignIn using the code above.
7. User is forwarded to the site's main page.
8. The site receives the request to load the main page. This is where things sometimes go awry.
   The User.Identity at this point is of type WindowsIdentity with AuthenticationType set to Negotiate, and NOT as I would expect, the ClaimsIdentity created in the SignIn method above.
   The site prepares the main page for the user by calling @AntiForgery.GetHtml() in the view. This is done to create a new AntiForgery token with the logged in user's details. The token is created with the WindowsIdentity
9. As the main page loads, ajax requests made to the server arrive with ClaimsIdentity! The first POST request to arrive therefore inevitably causes an AntiForgeryException where the anti-forgery token it sent is "for a different user".

Refreshing the page causes the main page to load with ClaimsIdentity and allows POST requests to function.

Second, related, problem: At any point after the refresh, once things are supposedly working properly, a POST request may arrive with WindowsIdentity and not with ClaimsIdentity, once again throwing an AntiForgeryException.

• It is not any specific post request,
• it is not after any specific amount of time (may be the first/second request, may be the hundredth),
• it is not necessarily the first time that specific post request got called during that session.

I feel like I'm either missing something regarding the User.Identity or that I did something wrong in the log-in process... Any ideas?

Note: Setting AntiForgeryConfig.SuppressIdentityHeuristicChecks = true; allows the AntiForgery.Validate action to succeed whether WindowsIdentity or ClaimsIdentity are received, but as is stated on MSDN:

Use caution when setting this value. Using it improperly can open security vulnerabilities in the application.

With no more explanation than that, I don't know what security vulnerabilities are actually being opened here, and am therefore loathe to use this as a solution.

Answer 1

Turns out the problem was the ClaimsPrincipal support multiple identities. If you are in a situation where you have multiple identities, it chooses one on its own. I don't know what determines the order of the identities in the IEnumerable but whatever it is, it apparently does necessarily result in a constant order over the life-cycle of a user's session.

As mentioned in the asp.net/Security git's Issues section, NTLM and cookie authentication #1467:

Identities contains both, the windows identity and the cookie identity.

and

It looks like with ClaimsPrincipals you can set a static Func<IEnumerable<ClaimsIdentity>, ClaimsIdentity> called PrimaryIdentitySelector which you can use in order to select the primary identity to work with.

To do this, create a static method with the signature:

static ClaimsIdentity MyPrimaryIdentitySelectorFunc(IEnumerable<ClaimsIdentity> identities)

This method will be used to go over the list of ClaimsIdentitys and select the one that you prefer.
Then, in your Global.asax.cs set this method as the PrimaryIdentitySelector, like so:

System.Security.Claims.ClaimsPrincipal.PrimaryIdentitySelector = MyPrimaryIdentitySelectorFunc;

My PrimaryIdentitySelector method ended up looking like this:

public static ClaimsIdentity PrimaryIdentitySelector(IEnumerable<ClaimsIdentity> identities)
{
    //check for null (the default PIS also does this)
    if (identities == null) throw new ArgumentNullException(nameof(identities));

    //if there is only one, there is no need to check further
    if (identities.Count() == 1) return identities.First();

    //Prefer my cookie identity. I can recognize it by the IdentityProvider
    //claim. This doesn't need to be a unique value, simply one that I know
    //belongs to the cookie identity I created. AntiForgery will use this
    //identity in the anti-CSRF check.
    var primaryIdentity = identities.FirstOrDefault(identity => {
        return identity.Claims.FirstOrDefault(c => {
            return c.Type.Equals(StringConstants.ClaimTypes_IdentityProvider, StringComparison.Ordinal) &&
                   c.Value == StringConstants.Claim_IdentityProvider;
        }) != null;
    });

    //if none found, default to the first identity
    if (primaryIdentity == null) return identities.First();

    return primaryIdentity;
}

[Edit]
Now, this turned out to not be enough, as the PrimaryIdentitySelector doesn't seem to run when there is only one Identity in the Identities list. This caused problems in the login page where sometimes the browser would pass a WindowsIdentity when loading the page but not pass it on the login request {exasperated sigh}. To solve this I ended up creating a ClaimsIdentity for the login page, then manually overwriting the the thread's Principal, as described in this SO question.

This creates a problem with Windows Authentication as OnAuthenticate will not send a 401 to request Windows Identity. To solve this you must sign out the Login identity. If the login fails, make sure to recreate the Login user. (You may also need to recreate a CSRF token)

Answer 2

I'm not sure if this will help, but this is how I've fixed this problem for me.

When I added Windows Authentication, it fluctuated between Windows and Claims identities. What I noticed is that GET requests get ClaimsIdentity but POST requests gets WindowsIdentity. It was very frustrating, and I've decided to debug and put a breakpoint to DefaultHttpContext.set_User. IISMiddleware was setting the User property, then I've noticed that it has an AutomaticAuthentication, default is true, that sets the User property. I changed that to false, so HttpContext.User became ClaimsPrincipal all the time, hurray.

Now my problem become how I can use Windows Authentication. Luckily, even if I set AutomaticAuthentication to false, IISMiddleware updates HttpContext.Features with the WindowsPrincipal, so var windowsUser = HttpContext.Features.Get<WindowsPrincipal>(); returns the Windows User on my SSO page.

Everything is working fine, and without a hitch, there are no fluctuations, no nothing. Forms base and Windows Authentication works together.

services.Configure<IISOptions>(opts =>
{
    opts.AutomaticAuthentication = false;
});