Base64Url.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ryadel.Components.Security
{
    /// <summary>
    /// Base64Url encoder/decoder
    /// </summary>
    public static class Base64Url
    {
        /// <summary>
        /// Encodes the specified byte array.
        /// </summary>
        /// <param name="arg">The argument.</param>
        /// <returns></returns>
        public static string Encode(byte[] arg)
        {
            var s = Convert.ToBase64String(arg); // Standard base64 encoder

            s = s.Split('=')[0]; // Remove any trailing '='s
            s = s.Replace('+', '-'); // 62nd char of encoding
            s = s.Replace('/', '_'); // 63rd char of encoding

            return s;
        }

        /// <summary>
        /// Decodes the specified string.
        /// </summary>
        /// <param name="arg">The argument.</param>
        /// <returns></returns>
        /// <exception cref="System.Exception">Illegal base64url string!</exception>
        public static byte[] Decode(string arg)
        {
            var s = arg;
            s = s.Replace('-', '+'); // 62nd char of encoding
            s = s.Replace('_', '/'); // 63rd char of encoding

            switch (s.Length % 4) // Pad with trailing '='s
            {
                case 0: break; // No pad chars in this case
                case 2: s += "=="; break; // Two pad chars
                case 3: s += "="; break; // One pad char
                default: throw new Exception("Illegal base64url string!");
            }

            return Convert.FromBase64String(s); // Standard base64 decoder
        }
    }
}