Your webserver serves a page that grabs the token then relays it from the frontend to the backend. Something like this is a rough example.
if (document.location.hash && document.location.hash != '') {
var parsedHash = new URLSearchParams(window.location.hash.substr(1));
if (parsedHash.get('access_token')) {
var access_token = parsedHash.get('access_token');
fetch(
'http://localhost/?my_token=' + access_token
)
.then(resp => {})
.catch(err => {
console.log(err);
});
}
}
Sub http://localhost/ for whatever http://localhost:1234/ whatever port number you spawn up on