public Task <(string hash, string signedTransaction)> SignTransactionAsync(
string transactionContext, IReadOnlyList <string> privateKeys)
{
if (privateKeys.Count != 1)
{
throw new ArgumentException("Only single private key is allowed");
}
var key = KeyPair.CreateFromPrivateKey(privateKeys[0]);
var signedTransaction = TransferTransaction.FromJson(transactionContext).SignWith(key);
var result = (
signedTransaction.Hash,
signedTransaction.ToJson()
);
return(Task.FromResult(result));
}