Multiple auth Soroban contract call

multiauth.ts

import { Keypair, Transaction, hash, scValToNative, xdr } from 'stellar-base';
// generated from Typescript bindings
import { Client, networks } from 'contract-client';

function getClientForKeypair(keys: Keypair) {
  return new Client({
    contractId: networks.testnet.contractId,
    networkPassphrase: networks.testnet.networkPassphrase,
    rpcUrl: 'https://soroban-testnet.stellar.org',
    publicKey: keys.publicKey(),
    signTransaction: async (tx: string, opts) => {
      const txFromXDR = new Transaction(tx, opts.networkPassphrase);

      txFromXDR.sign(keys);

      return txFromXDR.toXDR();
    },
    signAuthEntry: async (entryXdr, opts) => {
      return keys
        .sign(hash(Buffer.from(entryXdr, 'base64')))
        .toString('base64');
    },
  });
}

const buy = async (mft: string, user?: User) => {
  const contract = getClientForKeypair(sourceKeys);

  // get mft issuer with our logic
  let tx = await contract.buy(
    {
      buyer: buyerKeys.publicKey(),
      mft: mft,
      amount: BigInt(10),
    },
    { fee: 100000000 }
  );

  console.log(await tx.needsNonInvokerSigningBy());

  const jsonFromRoot = tx.toJSON();

  console.log(tx.simulationData.transactionData.resources);

  const buyerClient = getClientForKeypair(buyerKeys);

  const txBuyer = buyerClient.fromJSON['buy'](jsonFromRoot);

  await txBuyer.signAuthEntries();

  const jsonFromBuyer = txBuyer.toJSON();

  const txRoot = contract.fromJSON['buy'](jsonFromBuyer);

  const result = await txRoot.signAndSend();

  // console.log('send res', result.sendTransactionResponseAll);
  // console.log('get res', result.getTransactionResponseAll);
  const getRes = result.getTransactionResponse as any;

  console.log(getRes.resultMetaXdr.toXDR('base64'));

  xdr.TransactionMeta.fromXDR(getRes.resultMetaXdr.toXDR('base64'), 'base64')
    .v3()
    .sorobanMeta()
    ?.diagnosticEvents()
    .forEach((event) => {
      // console.log(event);
      // console.log('event', event.event().body().v0().data().toXDR('base64'));
      console.log(scValToNative(event.event().body().v0().data()));
    });

  return result.getTransactionResponse;
};