The code sample had multiple problems. The most important one was that
it did not run because the call to `checkIfUpdated` was incorrect and
the code didn't take into account that a DOMException is thrown when
trying to read `popup.location.href` before the redirect happened. Apart from
that I added url encoding of the query parameters and some simple sanity
checks on the received `token` and `assertion` values in order to make
the sample a bit more robust.