How to update a claim in ASP.NET Identity?

I created a Extension method to Add/Update/Read Claims based on a given ClaimsIdentity

namespace Foobar.Common.Extensions
{
    public static class Extensions
    {
        public static void AddUpdateClaim(this IPrincipal currentPrincipal, string key, string value)
        {
            var identity = currentPrincipal.Identity as ClaimsIdentity;
            if (identity == null)
                return;

            // check for existing claim and remove it
            var existingClaim = identity.FindFirst(key);
            if (existingClaim != null)
                identity.RemoveClaim(existingClaim);

            // add new claim
            identity.AddClaim(new Claim(key, value));
            var authenticationManager = HttpContext.Current.GetOwinContext().Authentication;
            authenticationManager.AuthenticationResponseGrant = new AuthenticationResponseGrant(new ClaimsPrincipal(identity), new AuthenticationProperties() { IsPersistent = true });
        }

        public static string GetClaimValue(this IPrincipal currentPrincipal, string key)
        {
            var identity = currentPrincipal.Identity as ClaimsIdentity;
            if (identity == null)
                return null;

            var claim = identity.Claims.FirstOrDefault(c => c.Type == key);
            return claim.Value;
        }
    }
}

and then to use it

using Foobar.Common.Extensions;

namespace Foobar.Web.Main.Controllers
{
    public class HomeController : Controller
    {
        public ActionResult Index()
        {
            // add/updating claims
            User.AddUpdateClaim("key1", "value1");
            User.AddUpdateClaim("key2", "value2");
            User.AddUpdateClaim("key3", "value3");
        }

        public ActionResult Details()
        {
            // reading a claim
            var key2 = User.GetClaimValue("key2");          
        }
    }
}