Chapter 1 What’s New for FortiOS 5.2.1 : Authentication : Single Sign-On for Guest Accounts
  
Single Sign-On for Guest Accounts
The default FSSO_Guest_Users group has changed to SSO_Guest_Users. This group supports guests using both Fortinet Single Sign-On (FSSO) and RADIUS Single Sign-On (RSSO).
Users can also now be added to this group SSO_Guest_group using the CLI.
Syntax
config user group
edit SSO_Guest_group
set member <names>
end
end