You have to set the Authorization
field in the header.
It contains the authentication type Basic
in this case and the username:password
combination which gets encoded in Base64:
var username="Test";
var password = '123';
var auth="Basic " + Buffer.from(username + ':' + password).toString('base64');
// new Buffer() is deprecated from v6
// auth is: 'Basic VGVzdDoxMjM='
var header = {'Host': 'www.example.com', 'Authorization': auth};
var request = client.request('GET', "https://stackoverflow.com/", header);