Many businesses and organizations use Active Directory or other LDAP-based authentication systems, and many web applications (like Drupal) can easily integrate with them for authentication and user account provisioning.
The Kerberos Module for Apache allows users to be automatically logged into your web application, by passing through their credentials behind the scenes. This makes for a seamless user experience—the user never needs to log into your web application if the user is authenticated on his local machine.
A standard configuration for Kerberos authentication inside your Apache configuration file looks like:
# By default, allow access to anyone.
Allow from All
# Enable Kerberos authentication using mod_auth_kerb.
AuthName "Your Web Application"