Tumblr API - how to get posts of a private blog using NodeJS?

I get a library named "tumblrwks" ( https://github.com/arkxu/tumblrwks ) that connect to the tumblr API using nodejs and i works, but the problem is i want get them form a private blog and for that i need the OAuth request.

How i can get the OAuth ( oauth_token & oauth_secret ) in Tumblr ?

this is the code that i want to complet with the OAuth, please help me

var Tumblr = require('tumblrwks');

/*
  You can get the consumerKey and consumerSecret by registing a tumblr app: http://www.tumblr.com/oauth/apps
*/

var tumblr = new Tumblr(
  {
    consumerKey: 'YOUR_CONSUMER_KEY',
    consumerSecret: 'YOUR_CONSUMER_SECRET',
    accessToken: 'ACCESS_TOKEN',
    accessSecret: 'ACCESS_SECRET'
  }, "void2012.tumblr.com"
  // specify the blog url now or the time you want to use
);

tumblr.get('/info', {hostname: 'void2012.tumblr.com'}, function(json){
  console.log(json);
});