Chapter 3 Authentication for FortiOS 5.0 : Users and user groups : User groups : Configuring Peer user groups
  
Configuring Peer user groups
Peer user groups can only be configured using the CLI. Peers are digital certificate holders defined using the config user peer command. The peer groups you define here are used in dialup IPsec VPN configurations that accept RSA certificate authentication from members of a peer certificate group. For more information, see “Authenticating IPsec VPN users with security certificates”.
To create a peer group - CLI example
config user peergrp
edit vpn_peergrp1
set member pki_user1 pki_user2 pki_user3
end