Adding a request header on beforeSend

Im using storageManager remote but the site has csrf token

beforeSend: function (t) {
    var token = $('meta[name="csrf_token"]').attr('content');
                    if (token) {
                        return t.setRequestHeader('X-CSRF-TOKEN', token);
                    }
     },

Gives an error "Uncaught TypeError: Cannot read property 'setRequestHeader' of undefined" obviously because t is undefined, how can I pass the headers into beforeSend without changing grapesjs