I am passing my tokens to local storage, and I would like to retrieve them and authorize whether the user is able to enter the page or it is forbidden upon loading a new page. The thing is I do not know how to retrieve the token, I heard that passing/receiving it through headers would be necessary but I do not know how that process is done. Thank you in advance for your help :) This is my code for passing the token to the local storage:

    function login(e){
    e.preventDefault();

    let username = document.getElementById('username').value;
    let password = document.getElementById('password').value;

    var details = {
    'username': username,
    'password': password,
  };

    var formBody = [];
    for (var property in details) {
      var encodedKey = encodeURIComponent(property);
      var encodedValue = encodeURIComponent(details[property]);
      formBody.push(encodedKey + "=" + encodedValue);
  }
    formBody = formBody.join("&");

    

    fetch('http://localhost:8080/login', {
      method: "POST",
      headers: {
        'Content-Type': 'application/x-www-form-urlencoded;charset=UTF-8'},
      body: formBody
  })
    .then((res) => {
      if(res.status == '200'){
        return res.json();
      }else{
        alert("Incorrect login information")
      }
  })
    .then((data) => {
      let jwt = data.access_token

      let jwtData = jwt.split('.')[1]
      let decodedJwtJsonData = window.atob(jwtData)
      let decodedJwtData = JSON.parse(decodedJwtJsonData)

      let role = decodedJwtData.roles

      if(role == "ADMIN"){
        window.localStorage.setItem('access_token', data.access_token);
        window.localStorage.setItem('refresh_token', data.refresh_token);
        // Here would go the call to another site.

      }
      if(role == "MODERATOR"){
        window.localStorage.setItem('access_token', data.access_token);
        window.localStorage.setItem('refresh_token', data.refresh_token);
        location.href = "moderatorHomepage.html";
      }
        window.localStorage.setItem('access_token', data.access_token);
        window.localStorage.setItem('refresh_token', data.refresh_token);
      if(role == "CUSTOMER"){
        location.href = "homepage.html";
      }
      
  })
    .catch(err =>{
      console.error(err.message);
  })