private string GetSignature(Track track, string salt)
        {
            // https://en.wikipedia.org/wiki/Hash-based_message_authentication_code
            throw new NotImplementedException("Implement HMAC-SHA1!");

            var songIdEncoded = Encoding.UTF8.GetBytes(track.StoreId);
            var saltEncoded   = Encoding.UTF8.GetBytes(salt);
            var hmacKey       = Encoding.UTF8.GetBytes(Key);

            var data = DataTypeUtils.CombineBytes(songIdEncoded, saltEncoded);

            var hmac = WinRTCrypto.HashAlgorithmProvider.OpenAlgorithm(HashAlgorithm.Sha1);

            var sig = DataTypeUtils.ToUrlSafeBase64(hmac.HashData(data));

            return(sig);
        }