Authentication modules are set for realms by first adding the Core Authentication service to the realm.
Navigate to the realm for which you wish to add the Authentication Chain.
Click the Authentication tab.
Select the Default Authentication Chain from the pull down menu.
Select the Administrator Authentication Chain from the pull down menu. This attribute can be used if the authentication module for administrators needs to be different from the module for end users. The default authentication module is LDAP.
Once you have defined the authentication chains, click Save.