Google App Script

function myFunction() {
  return [
    [1,2,3],
    ['a','b','c']
  ];
}
var siteUrl = 'http://www.heilsueflandi.is';

function getData(cookie) {
  var newOptions = {
    'headers': {
      Cookie: cookie
    }
  };
  var response = UrlFetchApp.fetch(siteUrl + "/umbraco/backoffice/UmbracoApi/Authentication/IsAuthenticated", newOptions);

  var sheet = SpreadsheetApp.getActiveSheet();
  sheet.appendRow(['Authenticated:', response.getContentText()]);
}

function authenticate(username, password) {
  var data = JSON.stringify({"username":username,"password":password});

  var options = {
    'method': 'post',
    'contentType': 'application/json',
    'payload': data,
    'muteHttpExceptions': true,
  };

  var response = UrlFetchApp.fetch(
    siteUrl + "/umbraco/backoffice/UmbracoApi/Authentication/PostLogin",
    options
  );

  var responseCode = response.getResponseCode();
  if (responseCode >= 200 && responseCode < 300) {
    var headers = response.getHeaders();
    getData(headers['Set-Cookie']);
  }
  else {
    doUsernamePrompt('Error authenticating, likely a user/pass error. Please try again\n');
  }
}

function usernamePrompt() {
   doUsernamePrompt('');
}

function doUsernamePrompt(additionalText) {
  var ui = SpreadsheetApp.getUi();
  var result = ui.prompt(additionalText + 'Username:');

  // Process the user's response.
  var button = result.getSelectedButton();
  var username = result.getResponseText();

  if (!username.length) {
    usernamePrompt();
  }

  passwordPrompt(username);
}

function passwordPrompt(username) {
  var ui = SpreadsheetApp.getUi();
  var result = ui.prompt('Password:');

  // Process the user's response.
  var button = result.getSelectedButton();
  var password = result.getResponseText();

  if (!password.length) {
    passwordPrompt(username);
  }

  authenticate(username, password);
}