The Native realm is a special realm that provides a bridge between the core ACL-based authentication model and the J2SE/Servlet authentication model. Use the Native realm for Java web applications to have the ACL subsystem perform the authentication (instead of having the Java web container do so) and yet have this identity available for Java web applications.
When an authentication operation is invoked, the Native realm delegates this authentication to the core authentication subsystem. From the user’s perspective this is essentially equivalent to, for example, the LDAP realm delegating authentication to the configured LDAP server. When group membership queries are processed by the Native realm, they are also delegated to the core authentication subsystem. From the Java web modules and the developers perspective, the Native realm is no different from any of the other Java realms which are available for use with web modules.
Additional configuration is required as the Native realm delegates the authentication to the core, . For more information, see Configuring the Native Realm.
The Sun Java System Web Server 6.1 Programmer’s Guide to Web Applications provides a detailed discussion on J2SE security realms and the configuration parameters you can use to configure security realms.