Login into a website using google apps script and click through to scrape data

Question

I want to login to a website and navigate to a specific page to scrape the data. I am planning on using scraping (not API at the moment) and for learning purpose I plan on doing it on my stackoverflow account to extract how my reputation score has changed over time and on which topic.

And, I am using google apps script as a programming language, also for the learning purpose.

I am using the below given code for login:

function stackLogin() {

  var url = "https://stackoverflow.com/users/login?ssrc=head";
  //var url = "https://stackoverflow.com/";

  var payload = {
    "email":"myLogin",
    "password":"myPassword"
  };


  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);  
}

When I use:

url = "https://stackoverflow.com/users/login?ssrc=head"

I get "response code = 302" but the "response html" is very short. I also see that a new login ip appears on StackExchange OpenID .

But, if I use:

url = "https://stackoverflow.com"

I get "response code = 200" and the "response html" is very long. I also see that a new login ip does not appear on StackExchange OpenID.

Question 1) So, the login was only possible by url = "https://stackoverflow.com/users/login?ssrc=head", rite ??

Question 2) If I am able to login I want to click "my profile avatar button"

which takes me to the "user profile/summary" page where I want to click "Reputation"

which takes me to "Reputation log page" where I have summary of all the reputation I have received by date and topics.

Now, I want to extract these reputation values as table.

I can scrape the data by inspecting the class values of these reputation logs if I can pull the HTML page.
The main problem I have though is : How do I click through different buttons (after successfully logging in) to get to that "Reputation log" page.