private async Task CreateSignatureAsync(SortedDictionary <string, string> data)
{
// Combine as string
var source = smsKey + "&" + data.JoinAsString() + smsKey;
// Calculate signature
var signatureBytes = await CryptographyUtils.MD5Async(source);
data["signature"] = Convert.ToHexString(signatureBytes).ToLower();
}
