Chapter 4 Authentication : Configuring authenticated access : Authentication in security policies : NTLM authentication : NTLM guest access
  
NTLM guest access
Guest profile access may be granted to users who fail NTLM authentication, such as visitors who have no user credentials on the network. To allow guest user access, edit the FSSO security policy in the CLI, like this:
config firewall policy
edit 4
set ntlm enable
set ntlm-guest enable
end