Node.js webscraping authentication

I can do this in Python and Ruby, but I wanted to give Node.js a shot and so far the whole scraping process is confusing. I am having trouble with the post request for logging into a site to scrape the data. Here is the code:

var request = require('request');
var cheerio = require('cheerio');

var credentials = {
    username: 'kevin',
    password: 'secret'
};

request.post({
    uri: 'http://yourwebsite.com/login',
    headers: { 'content-type': 'application/x-www-form-urlencoded' },
    body: require('querystring').stringify(credentials)
}, function(err, res, body){
    if(err) {
        callback.call(null, new Error('Login failed'));
        return;
    }
});

So say I want to scrape after I logged in. Am I replacing the username and password under credentials with the field id? or is it the field name? Also, where is the part where I am hitting submit (button) on form?

Edit: Here is the full code on some other site I tried on:

var cheerio = require('cheerio');
var request = require('request');


var credentials = {
    acct: '....',
    pw: '.....'
};

request.post({
    uri: 'https://news.ycombinator.com/login?whence=news',
    headers: { 'content-type': 'application/x-www-form-urlencoded' },
    body: require('querystring').stringify(credentials)
}, function(err, res, body){    

    request('https://news.ycombinator.com', function(err, res, body) {
        if(err) {
            callback.call(null, new Error('Request failed'));
            return;
        }

        var $ = cheerio.load(body);
        var text = $('.pagetop').text();

        console.log(text);
    });
});