Squid can forward https:// request to peer

In cache_peer options:


cache_peer parent.foo.net       parent    3128  3130  proxy-only front-end-https

In the help doc, he says:

use front-end-https to enable the "Front-End-Https: On"
     header needed when using Squid as a SSL frontend in front
     of Microsoft OWA. See MS KB document Q307347 for details
     on this header. If set to auto the header will
     only be added if the request is forwarded as a https://
     URL.