Hi I'm in trouble using fetch function, in this moment I wanna change the headers after a login using the token 'l' so it gives me success if is a real user. This is the code:

var l; //variable l use to put the token in the future

Login

const login = document.getElementById('login');

    const nome = document.getElementById('lnome');
    const pass = document.getElementById('lpass');

    const item = {
        Username: nome.value.trim(),
        Password: pass.value.trim()
    };

    fetch(uri_2, {
        credentials: 'include',
        method: 'POST',
        headers: {
            'Accept': 'application/json',
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(item)
    })
        .then(response => {
           //check in the response if is a user, otherwise do catch     
        })
        .then((res) => {
            nome.value = '';
            pass.value = '';

            window.alert('Login Bem Sucedido :');


            //HERE I HAVE PROBLEM PUT THE TOKEN, THIS CODE IS WRONG               

            //setRequestHeader("Authorization", 'Bearer ' + l);
            headers: new Headers({
                'Authorization': 'Basic ' + btoa('username:password'),
                'Content-Type': 'application/x-www-form-urlencoded'
            }), 

            //HERE I PUT THE TOKEN IN A VAR L

            l = res;
            window.location.href = url_1;

        })
       
        .catch(error => {
            //here i have a bunch of alerts to check if is a valid user
        });
}

Page List after login

$(function () {
    var $users_A = $('#users_A');
    debugger;
        $.ajax({
            url: uri_3_2,
            type: 'GET',
            dataType: 'json',

            //HERE IS WHEN I NEED TO PUT THE TOKEN
            beforeSend: function (request) {
                request.setRequestHeader("Authorization",'Bearer '+l);
            },

            success: function (data) {
                console.log('Sucess YAYYYYYYYY');
            },
            error: function (xhr, textStatus, errorThrown) {
                console.log('Error in Operation');
                
            }
        });
    });

I did debugger in both functions and for my surprise, before the method ajax is call, I can put the token into the variable l BUT after the method ajax, it is undefined the token and I don´t understand why, its because of using fetch and in the other hand using ajax, its because of the headers of the fetch or its other error?

Any answer is welcome.