Chapter 10 Install and System Administration for FortiOS 5.0 : Basic Administration : Administrators : Security Precautions : HTTPS redirect
  
HTTPS redirect
When selecting port numbers for various protocols, you can also enable or disable the Redirect to HTTPS option. When enabled, if you select the Administrative Access for an interface to be only HTTP, HTTPS will automatically be enabled, allowing the administrator access with either HTTP or HTTPS. The administrator can then log in using HTTPS for better security.
Note that if an SSL VPN is also configured for the same port, the SSL connection is over the HTTPS protocol. In these situations, the FortiGate unit will not redirect an HTTP address to the SSL VPN HTTPS address. Ideally, the administrator should not have the management address and an SSL VPN portal on the same interface.