ClaimExtensions.cs

using System.Linq;
using System.Security.Claims;
using System.Security.Principal;

namespace Infrastructure.Claims
{
    public static class ClaimExtensions
    {
		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));
		}

		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;
		}
	}
}