Chapter 3 Authentication for FortiOS 5.0 : Authentication servers : LDAP servers : Example of LDAP to allow Dial-in through member-attribute - CLI : Configuring LDAP group settings
  
Configuring LDAP group settings
A user group that will use LDAP must be configured. This example adds the member ldap to the group which is the LDAP server name that was configured earlier.
To configure LDAP group settings - CLI
config user group
edit "ldap_grp"
set member "ldap"
config match
edit 1
set server-name "ldap"
set group-name "TRUE"
next
end
end
Once these settings are in place, users can authenticate.