With browser authentication selected (used by the default login page), the task of authenticating a user is delegated to the browser. On your first visit, the browser will dutyfully ask the user for a username and password using a typical browser popup.
Here's the catch: in most browsers, that popup includes a checkbox and an explanation similar to "Remember my credentials". If you just mark this checkbox once and perform a successful login, the browser will remember your credentials for this web site and log you in automatically every time you visit that particular URL.
You can only tell your user to clear the browser cache (including the list of stored username/password combinations) and not to mark this checkbox ever again. You should only use the default login page if you want to use SSO or get as near to it as possible.