title: AccessDeniedHandler with redirect to login page
body: <p>When (in Spring Security / MVC) the access to a page is denied, as the user has not enough privileges (though he is authenticated), I need to offer to login as another user via showing the login page (instead of the standard behaviour of showing a 403 access denied page).<br>
  I can write an <code>AccessDeniedHandler</code>, that redirects to the login page. But how will Spring Security react, when it finds out, that there is alrady another user logged in? Can I somehow logout the old user when the new one has successfully authenticated?</p>