Scrape data behind login

I am super new to using GAS and Cheerio to scrape data.

I want the data on this page:

https://archiveofourown.org/users/[USERNAME]/stats

I cannot figure out how to get the script (below) working to log in.

function ao3Login() {

  var url = "https://archiveofourown.org/users/login";


  var payload = {
    "user[login]":"username",
    "user[password]":"password"
  };


  var opt = {
    "payload":payload,
    "method":"post",
    "followRedirects": false
  };  

  var response = UrlFetchApp.fetch(url, opt);
  var sessionDetails = response.getAllHeaders()['Set-Cookie'];
  var header = {
    'Cookie': sessionDetails[1]
  };  

  Logger.log(response.getResponseCode()); 
  Logger.log(response);  
}