An unauthenticated request to a deep link such as /admin/dashboard was
redirected to /, the user login, instead of the admin login. protect_route
always sent unauthenticated visitors to /.
Pick the login page from the request path: /admin/* redirects to /admin,
/domainadmin/* to /domainadmin, everything else to / as before.
Fixes#7284
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>