server/bitwarden_license/src/Sso/Utilities/ClaimsExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Security.Claims;
using System.Text.RegularExpressions;

namespace Bit.Sso.Utilities
{
    public static class ClaimsExtensions
    {
        private static readonly Regex _normalizeTextRegEx =
            new Regex(@"[^a-zA-Z]", RegexOptions.CultureInvariant | RegexOptions.Singleline);

        public static string GetFirstMatch(this IEnumerable<Claim> claims, params string[] possibleNames)
        {
            var normalizedClaims = claims.Select(c => (Normalize(c.Type), c.Value)).ToList();

            // Order of prescendence is by passed in names
            foreach (var name in possibleNames.Select(Normalize))
            {
                // Second by order of claims (find claim by name)
                foreach (var claim in normalizedClaims)
                {
                    if (Equals(claim.Item1, name))
                    {
                        return claim.Value;
                    }
                }
            }
            return null;
        }

        private static bool Equals(string text, string compare)
        {
            return text == compare ||
                (string.IsNullOrWhiteSpace(text) && string.IsNullOrWhiteSpace(compare)) ||
                string.Equals(Normalize(text), compare, StringComparison.InvariantCultureIgnoreCase);
        }

        private static string Normalize(string text)
        {
            if (string.IsNullOrWhiteSpace(text))
            {
                return text;
            }
            return _normalizeTextRegEx.Replace(text, string.Empty);
        }
    }
}