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David Vassallo's Blog

If at first you don't succeed; call it version 1.0

Tag Archives: proxy

Update: SQUID transparent SSL interception : Squid v3.2

In order to keep this blog post a bit more relevant, there have been some improvements since that post was written. Squid v3.2 has been released earlier this year, making ssl interception more seamless and easier. The new features for HTTPS interception can be found while reading through the man page for http_port:


More specifically:

1. The “transparent” keyword has been changed to “intercept“:

           intercept    Rename of old 'transparent' option to indicate proper functionality.

INTERCEPT is now better described as:

intercept	Support for IP-Layer interception of
			outgoing requests without browser settings.
			NP: disables authentication and IPv6 on the port.

2. In order to avoid more certificate errors when intercepting HTTPS sites, squid now can dynamically generate SSL certificates, using generate-host-certificates. This means the CN of the certificate should now match that of the origin server, though the certificate will still be generated using SQUID’s private key:

SSL Bump Mode Options:
	    In addition to these options ssl-bump requires TLS/SSL options.

			Dynamically create SSL server certificates for the
			destination hosts of bumped CONNECT requests.When 
			enabled, the cert and key options are used to sign
			generated certificates. Otherwise generated
			certificate will be selfsigned.
			If there is a CA certificate lifetime of the generated 
			certificate equals lifetime of the CA certificate. If
			generated certificate is selfsigned lifetime is three 
			This option is enabled by default when ssl-bump is used.
			See the ssl-bump option above for more information.

Looks like the above is an offshoot of the excellent work here: http://wiki.squid-cache.org/Features/DynamicSslCert

Make sure to use the above two features for smoother HTTPS interception – though remember, always warn users that SSL traffic is being decrypted, privacy is a highly-valued right…

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Preserving client IP w/ apache reverse proxy

We recently had a scenario where an apache reverse proxy needed to be deployed in front of a pair of tomcat servers. Due to security concerns, this reverse proxy was hosting mod_security and acting as a web application firewall (WAF)

However, a critical requirement was that the tomcat applications would be able to see the original IP address of the client. This presented a problem because unlike squid, apache has no configurable option to act as a fully transparent proxy. In other words, once traffic was redirected through the apache reverse proxy, the traffic forwarded to the tomcat server was forwarded with it’s source IP address changed to the proxy, effectively hiding the public IP the client used to connect to the site.

The first solution that sprang to mind was the “X-Forwarded-For” headers, which is an HTTP header inserted into the original HTTP GET request whose value is equal to the client’s public IP. Turns out apache reverse proxy inserts this header by default, and even so the tomcat application could not extract the client’s IP. We somehow needed to instruct the tomcat server itself to provide the application with the correct client IP.

The solution that worked in my case was the RemoteIP tomcat valve. Official documentation lives here:


It’s quite simple to configure in that all that needs to be done is to modify tomcat server.xml to recognise original client IP rather than the proxy IP by adding the following to server.xml:

<Valve className="org.apache.catalina.valves.RemoteIpValve"
internalProxies="127\.0\.0\.1" />

make sure to change to the address of the apache reverse proxy.

The application could now recognise the original client IP.


PS as per the tomcat documentation, the apache equivalent of the above method is using the mod_remoteip


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