Chapter 1 What’s New for FortiOS 5.0 : New features in FortiOS 5.0 Patch 3 : SSO Authentication failover for the Explicit Web Proxy
  
SSO Authentication failover for the Explicit Web Proxy
SSO authentication failover for the Explicit Web Proxy is now available, allowing two authentication methods to be configured. If the Single Sing-On Method fails, the FortiGate unit will use the Default Authentication Method.
To configure failover, the explicit web proxy must first be enabled.
Figure 14: Configuring SSO authentication failover for the explicit web proxy