Soap client with Node and strong-soap returning error with cerficate

I am using strong-soap (but with node-soap is the same result) node module to connect with soap services.

In the first step I am creating the client and trying to connect one method in this case "doLogin" method.

My code is:

soap.createClient(url, clientOptions, (err, client) => {
var loginApi = { UserName: "xxxx", Password: "xxxxxx" };
var loginUser = {
  userName: "comercial@xxxxx.com"
};
client.addSoapHeader(header);
//client.setSecurity(new soap.BasicAuthSecurity(loginApi));
// we now have a soapClient - we also need to make sure there's no `err` here.
client.doLogin(loginUser, (err, result) => {
  //'result' is the response body
  console.error(err);
  console.log("Result: \n" + JSON.stringify(result));
});

But the variable err is returning this error in the console:

{ Error: unable to verify the first certificate
    at TLSSocket.<anonymous> (_tls_wrap.js:1105:38)
    at emitNone (events.js:106:13)
    at TLSSocket.emit (events.js:208:7)
    at TLSSocket._finishInit (_tls_wrap.js:639:8)
    at TLSWrap.ssl.onhandshakedone (_tls_wrap.js:469:38) code: 
    'UNABLE_TO_VERIFY_LEAF_SIGNATURE' }

and result is undefined.

1. why is happening this error?
2. result is undefined by the error?

FIXED:

I have added correct certificates and rejectUnauthorized: false to create client and added "envelope" directive to the headers and now it is working.

I don´t like the instruction rejectUnauthorized: false by security topics and I would like to know how to remove this in production environment.

Thank you!!