You can configure Access Gateway to force the HTTP services to have the authentication cookie set with the keyword secure.
To enable this option, perform the following steps:
Click Devices > Access Gateways > Edit > Reverse Proxy / Authentication.
Select Enable Secure Cookies, then click OK > OK.
Update Access Gateway.
This option secures the cookie when Access Gateway is placed behind an SSL accelerator, such as the Cisco SSL accelerator, and Access Gateway is configured to communicate by using only HTTP.