Cool Solution - Squid as Reverse SSL Proxy

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Note: Cool Solutions are articles documenting additional functionality based on Univention products. Not all of the shown steps in the article are covered by Univention Support. For questions about your support coverage contact your contact person at Univention before you want to implement one of the shown steps.

Also regard the legal notes at Terms of Service.
Note: This article is not yet reviewed.
Produktlogo UCS Version 3.2
Produktlogo UCS Version 4.0

This article describes how to configure Squid3 as a reverse proxy with HTTPS and SSL support. This allows to proxy your secured application without exposing your Webserver to the outside or to loadbalance between multiple SSL Servers.

Requirements

To install Squid3 for UCS 3.2, execute the following command:

univention-install univention-squid

In addition you need the private key and the public certificate from the server you want to tunnel to. In the following we refer to the certificate as cert.pem,to the key as private.key and to the server you want to tunnel to as DSTHOST.

Note: Everything within a less-than sign (<) and a greater-than sign (>) must be replaced with your own values.

Note: Everything that is written cursive in the code boxes is a variable value and may be changed to own use.

Pre-Configuration

At first, the Apache Server must be stopped and disabled within its UCR variable. This is necessary to free the HTTPS port for Squid3

service apache2 stop
ucr set apache2/autostart="no"


Configure Squid

Afterwards the template file /etc/univention/templates/files/etc/squid3/squid.conf must be edited.

You should backup the original template file before making any changes:

cp /etc/univention/templates/files/etc/squid3/squid.conf /etc/univention/templates/files/etc/squid3/squid.conf.backup

To configure your reverse SSL proxy, add the lines below # reverse proxy to your configuration. A good placement for this is at the top of your configuration file (e.g. below # debug options).

...

print "#reverse SSL proxy"
print "https_port 443 cert=/path/to/cert.pem key=/path/to/private.key  defaultsite=<FQDN of DSTHOST> vhost"
print "cache_peer <IP of DSTHOST> parent 443 0 no-query proxy-only originserver ssl sslflags=DONT_VERIFY_PEER name=myHost"

print "#########"
print "# acl's #"
print "#########"

Remember the name you've given here, we need it later to configure the ACLs

Configure ACLs

After the reverse proxy is configured, the next step is to configure ACLs to define who is able to access your site and who is not. At first, we define an ACL for a network. A few ACLs are already defined in your configuration. To keep the configuration file human readable, we stick to the schema and add our changes into the correct sections.

To grant access to a whole network, add the following line to your config

...

print "acl myNetwork src <Network adress>/<Netmask>"

print "#########"
print "# rules #"
print "#########"
... 

Afterwards, the rules for our newly created ACL have to be defined

...

print "http_access allow myNetwork"
print "cache_peer_access myHost allow myNetwork"

print "# deny the rest"
print "http_access deny all"
print "http_reply_access allow all"
print "icp_access allow all"
...

Note: You can also set the rules for acl and http_access_allow via the ucr variable squid/allowfrom. If you do so, your network will be named dynamically, e.g. localnet1. For more than one network, you can simply write them all to squid/allowfrom, seperated with spaces. However, the rules for chache_peer_access and the rules for your reverse SSL proxy (https_port, cache_peer) have to be made directly in the config template.

Since Squid3 is a mighty product, we can't cover all cases you may want to define here. Please refer to the offical documentation in the Further Information section.

After your changes have been saved, your Squid3 configuration file needs to be commited and squid3 needs to be restarted:

ucr commit /etc/squid3/squid.conf
service squid3 restart

Afterwards your reverse proxy should be working.

Further Information

http://www.squid-cache.org/Doc/config/

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