Summary 
Current mod_proxy document does not include an example 
for https. I would suggest to add an example.

Reference
http://httpd.apache.org/docs/current/mod/mod_proxy.html

= Current =

Forward Proxy

ProxyRequests On
ProxyVia On

<Proxy *>
  Require host internal.example.com
</Proxy>

= Current =

= Suggested =

Forward Proxy

ProxyRequests On
ProxyVia On

<Proxy *>
  Require host internal.example.com
</Proxy>

<Proxy *:443>
  Require host internal.example.com
</Proxy>

= Suggested =

Also add following minor remarks, as well.

It is because the ssl communication should be established
between server and client, one can not specify access control 
with HTTPS protocol using detail URL.
(If you add "/" in <Proxy >, it does not work as you specified.)

Bad Example
<Proxy example.com:443/news/>

Good Example
<Proxy example.com:443>