var page = require('webpage').create();

page.settings.userName = 'your username here';

page.settings.password = 'your password here';

 var url = "your url comes here";
 var fs = require('fs');
 var path = 'index.html'; //here you can use a format of the file you want .json .txt etc.

 page.open(url, function (status) {
     if(status !== 'success')
         console.log('Connection failed, page was not loaded!');
     else
         var content = page.content;
         fs.write(path,content,'w')
         phantom.exit();
});