I use node js and express js. I want to make sure that if app.get is without a token parameter, then upload an html file with js that will pass the token. And if the token was passed, then show another html file.

But I do not know how to make a redirect from the client with the transfer of a header with a token

Server:

app.get("/admin-cp/:page", function (req, res) {
    const idToken = req.headers.authorization;
    if (!idToken)
    {

        return res.sendFile(path.join(initial_path, "admin-cp/loader.html"));
        //return res.status(401).send("Unauthorized")
    } 

    const sessionCookie = req.cookies.session || "";
    
    admin
        .auth()
        .verifySessionCookie(sessionCookie, true  )
        .then((userData) => {
            console.log("Logged in:", userData.email)
            console.log('Авторизован. Доступ в админ панель открыт')


            admin
            .auth()
            .verifyIdToken(idToken)
            .then((claims) => 
            {  
                if (claims.admin === true) 
                {    
                    console.log('Зашёл с правами администратора', req.params.page);
                    if (req.params.page === 'analytics')
                    {
                        console.log("Open analytics");
                        res.sendFile(path.join(initial_path, "admin-cp/main-admin_cp.html"));
                        //res.render(path.join(initial_path, "admin-cp/main-admin_cp.html"));
                        //res.redirect('/admin-cp/home');
                    }
                } 
                else if (claims.admin === false)
                {
                    console.log('Зашёл без прав администратора');
                    //res.sendFile(path.join(initial_path, "admin-cp/global_not_permission.html"));
                    res.redirect('/');
                }
            });
            
            
        })
        .catch((error) => {
            console.log('Не авторизован. Ошибка', error, ' отсутвует userData')
            res.redirect("/login");
        });

});

I tried to do with "fetch":

const res = await fetch('/admin-cp/analytics',  { headers: { authorization: idToken },  redirect: 'follow' })
  .then(res => {
    console.log(res);
    if (res.redirected) {
        document.location = res.url;
    }
  })

But after all the actions res.sendFile is not updated

help with any advice. please