Código explicado na LIVE #006: https://www.lucascaton.com.br/lives/

auth.js

document.addEventListener('DOMContentLoaded', () => {
  const uri = URI(window.location.href);
  const cookieName = uri.path() + '-auth';
  const authParam = uri.query(true)['auth'];
  const wbp = document.querySelector('head meta[name=wbp]').content;

  if (isUserAuthenticated()) {
    document.querySelector('body').setAttribute('style', ''); // Show page
  } else {
    if (checkWBP()) {
      document.cookie = cookieName + '=' + asciiToHexa(wbp);
    } else {
      window.location = window.location.href.replace(/(\/|\.html)?$/, '-inscricao/');
    }
  }

  if (authParam !== undefined) {
    // Removes 'auth' query string as user is already authenticated
    window.location = URI(window.location.href).removeSearch('auth').toString();
  }

  function isUserAuthenticated() {
    return getCookie(cookieName) === asciiToHexa(wbp);
  }

  // Copied from https://www.w3schools.com/js/js_cookies.asp
  function getCookie(cname) {
    var name = cname + '=';
    var decodedCookie = decodeURIComponent(document.cookie);
    var ca = decodedCookie.split(';');

    for(var i = 0; i < ca.length; i++) {
      var c = ca[i];
      while (c.charAt(0) == ' ') { c = c.substring(1); }
      if (c.indexOf(name) == 0) { return c.substring(name.length, c.length); }
    }

    return '';
  }

  function checkWBP() {
    return authParam === asciiToHexa(wbp);
  }

  function asciiToHexa(str) {
    var arr1 = [];

    for (var n = 0, l = str.length; n < l; n ++) {
      var hex = Number(str.charCodeAt(n)).toString(16);
      arr1.push(hex);
    }

    return arr1.join('');
  }
});