Make a user login prior to accessing anything on the site.

gistfile1.php

      global $user;
     
      /*
       * If the user is not logged in, require them to login prior to being
       * redirected to the form
       */
      if ($user->uid === 0 && arg(0) != 'user') {
        $dest = drupal_get_path_alias($_GET['q']);
        drupal_goto('user', array('query' => array('destination' => $dest)));
      }