Chapter 1 What’s New for FortiOS 5.2.1 : IPv6 : RSSO Support
  
RSSO Support
RADIUS Single Sign-On (RSSO) is supported in IPv6 and can be configured in the CLI. Fallthrough for unauthenticated
Syntax
config firewall policy6
edit <id>
set rsso enable
set fall-through-unauthenticated enable
end
end