Chapter 11 IPsec VPN for FortiOS 5.0 : L2TP and IPsec (Microsoft VPN) : Configuring the FortiGate unit : Configuring LT2P users and firewall user group
  
Configuring LT2P users and firewall user group
Remote users must be authenticated before they can request services and/or access network resources through the VPN. The authentication process can use a password defined on the FortiGate unit or an established external authentication mechanism such as RADIUS or LDAP.