How to use the libsodium-wrappers-sumo.crypto_sign_keypair function in libsodium-wrappers-sumo

web3,
  trustbase,
  inquirer
}) {
  const username = argv._.length > 1 ? argv._[1] : (await inquirer.prompt(usernamePrompt)).username
  if (username === '') {
    ora().fail('Invalid username')
    process.exit(1)
  }

  const usernameHash = web3.utils.sha3(username)

  let {
    publicKey,
    privateKey
  } = sodium.crypto_sign_keypair()
  publicKey = sodium.to_hex(publicKey)
  privateKey = sodium.to_hex(privateKey)

  const identityPath = path.resolve(os.homedir(), `.trustbase/idents/${usernameHash}.json`)
  if ((await fs.exists(identityPath))) {
    ora().info(`Found identity for '${username}' locally`)
    process.exit(0)
  }

  const records = (await fs.exists(RECORD_PATH)) ? (await fs.readJSON(RECORD_PATH)) : {}
  if (records[username]) {
    await checkRegister({
      argv: {
        _: ['check-register', username]
      },
      web3,

}
  const done = ret(cb);

  let payload, isk;
  [ payload ] = iparse(message);
  [ sk ]      = cparse(sk);

  switch (sk && Buffer.byteLength(sk)) {
    case sodium.crypto_sign_SECRETKEYBYTES:
      isk = sk;
      break;
    case sodium.crypto_sign_SEEDBYTES:
      isk = sodium.crypto_sign_seed_keypair(sk).privateKey;
      break;
    default:
      isk = sodium.crypto_sign_keypair().privateKey;
      sk  = sodium.crypto_sign_ed25519_sk_to_seed(isk);
  }

  let signature;
  try {
    signature = sodium.crypto_sign_detached(payload, isk);
  } catch(ex) {
    return done(new Error('Libsodium error: ' + ex));
  }

  return done(null, convert({
    alg:       'ed25519',
    sk:        sk,
    payload:   payload,
    signature: signature
  }));

return sodium.ready.then(() => {

    return (self.protocol() instanceof V1)
      ? self.inject(extcrypto.keygen(), (err) => { return done(err); })
      : self.inject(Buffer.from(sodium.crypto_sign_keypair().privateKey), (err) => { return done(err); });
  });
}

TransactionHelper.prototype.getProofs = function (provingServiceUri, callbackfn) {
  if (!this._anchor) throw new Error('Must call setAnchor() before getProofs()')

  var keyPair = sodium.crypto_sign_keypair()
  this.joinSplitPubKey = Buffer.from(keyPair.publicKey)
  this._joinSplitPrivKey = Buffer.from(keyPair.privateKey)

  for (var i = 0; i < this._jsouts.length; i += 2) {
    var inputs = [
      JSInput.dummy(),
      JSInput.dummy()
    ]

    var outputs = [
      this._jsouts[i],
      this._jsouts[i + 1] || JSOutput.dummy()
    ]

    var value = outputs.reduce(function (sum, output) { return sum + output.value }, 0)
    this.jss.push(JSDescription.withWitness(inputs, outputs, this.joinSplitPubKey, value, 0, this._anchor))