Chapter 9 High Availability for FortiOS 5.0 : HA and failover protection : Session failover (session pick-up) : SSL VPN session failover and SSL VPN authentication failover
  
SSL VPN session failover and SSL VPN authentication failover
Session failover is not supported for SSL VPN tunnels. However, authentication failover is supported for the communication between the SSL VPN client and the FortiGate unit. This means that after a failover, SSL VPN clients can re-establish the SSL VPN session between the SSL VPN client and the FortiGate unit without having to authenticate again.
However, all sessions inside the SSL VPN tunnel that were running before the failover are stopped and have to be restarted. For example, file transfers that were in progress would have to be restarted. As well, any communication sessions with resources behind the FortiGate unit that are started by an SSL VPN session have to be restarted.
To support SSL VPN cookie failover, when an SSL VPN session starts, the FGCP distributes the cookie created to identify the SSL VPN session to all cluster units.