On /admin (or any other configured URL for Integrated in the Symfony installation) only the Integrated scope is allowed. It is currently possible to go the admin after logging in on the website.
When a user is in the admin path (exluding the Integrated login page), check the scope. When the scope is not "Integrated" (a non-admin scope) redirect the user to the Integrated login page
Log in Integrated with an Integrated-scope user: should work
Log in Integrated with a website-scope user: should not work
Log in into the website a website-scope user: should work
After that go to the integrated content navigator: should redirect to the login form
Update security.yml with:
{ path: ^/admin, roles: IS_AUTHENTICATED_REMEMBERED, allow_if: 'integrated_scope().isAdmin() == true' }