htaccess style login for drupal
The Secure Site module could be the best choice:


  This module allows you to authenticate users with a browser-based
  password (HTTP Auth). You can restrict access to the site by role and
  choose to secure restricted pages or the entire site. This means the
  site will be inaccessible to search engines and other crawlers, but
  you can still allow access to certain users.


You can change the settings to use a page instead the popup. It's also possible to theme the login page - see the information here.