Flicker Effect when viewers redirect for authentication

We are using Windows Authentication (defined both in the instance and the site permissions).

When browsing to
https://mycompany.com/html5viewer
(assumng that there's a default configuration path)
would show the loading panel, then redirect
https://mycompany.com/html5viewer#gcx-SKQLnzKgkwLU2SLM5WpzjWrQPArf2qpqQ_k0-qfKt-CJWzDAAAMWD_LNFc7tVr0re7thimbAqQ
then looks like it redirects again and then ommiting the bit after the hash.

I know there is a way around that by sending users to Identity Server but that's not as tidy and users always return to the URL of the viewer (for example from their favourits or by sharing the address from the browser's address bar).

Would be nice if all of it can be doen in AJAX, invisible to the users.