In httpd.conf, make sure the Apache server only listens to port 80 on the localhost interface:
Listen 127.0.0.1:80
Also add, to the end of httpd.conf, the following (this is to support Touchstone):
ProxyPass /Shibboleth.sso/ [https://idp.mit.edu/Shibboleth.sso/] ProxyPassReverse /Shibboleth.sso/ [https://idp.mit.edu/Shibboleth.sso/] ProxyPass /Touchstone/ [https://idp.mit.edu/Touchstone/] ProxyPassReverse /Touchstone/ [https://idp.mit.edu/Touchstone/]
In squid.conf:
http_port ist-prod-pubs1.mit.edu:80 defaultsite=ist.mit.edu vhost http_access allow all cache_peer 127.0.0.1 parent 80 0 no-query originserver name=Accelerator