Chapter 3 Authentication for FortiOS 5.0 : SSO using a FortiAuthenticator unit
  
SSO using a FortiAuthenticator unit
If you use a FortiAuthenticator unit in your network as a single sign-on agent,
Users can authenticate through a web portal on the FortiAuthenticator unit.
Users with FortiClient Endpoint Security installed can be automatically authenticated by the FortiAuthenticator unit through the FortiClient SSO Mobility Agent.
The FortiAuthenticator unit can integrate with external network authentication systems such as RADIUS and LDAP to gather user logon information and send it to the FortiGate unit.