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);
}