Before you can configure these settings, you will need to have a proxy certificate
Navigate to Web Filter > Settings > Proxy Server > Transparent Proxy. Check the box next to Transparent proxy SSL to turn on Transparent proxy. Click Ok on the warning message. Click Save.
Note: Transparent proxy is only a feature of Web Filter 3.
Selective Transparent Proxy
Once Transparent proxy is enabled, you will have the option to make it selective by adding proxy hostnames. These hostnames will help you significantly lower the Transparent proxy load on your network. If you are only using Transparent proxy to decrypt SSL traffic, then you can simply add YouTube and Google domains to the Proxy Hostnames field.
After activating Transparent proxy, click the green plus icon to the right of Proxy Hostnames. The following will pop up. Add the hostname URL and an optional description and click Save. Entering one or more hostnames will cause proxying to be selective–that is, only requests made to these hostnames will be proxied.
You can delete a Proxy Hostname by clicking the gray “x” to the right of the hostname.
Watch the following video for an in-depth guide to enabling transparent SSL Proxy: