decode from URL-safe base64

gistfile1.txt

        public static byte[] FromUrlSafeBase64(string input)
        {
            // restore padding, if padding trimmed
            int padding = 4 - (input.Length%4);
            input = input.PadRight(padding, '=');

            char[] buf = Array.ConvertAll(Encoding.UTF8.GetBytes(input), c => (char) c);

            for (int i = 0; i < buf.Length; ++i)
                switch (buf[i]) {
                    case '-':
                        buf[i] = '+';
                        break;
                    case '_':
                        buf[i] = '/';
                        break;
                }

            return Convert.FromBase64CharArray(buf, 0, 0);
        }