Apache HTTPD/mod_proxy/Tomcat and SSL with client auth

This sounds similar to this question, where I've answered that it's not possible:

You can't just relay the SSL/TLS traffic to Tomcat from Apache. Eitheryour SSL connection ends at Apache, and then you should reverse proxythe traffic to Tomcat (SSL [between Httpd and Tomcat] is rarely useful in this case), or you makethe clients connect to Tomcat directly and let it handle the SSLconnection.

I admit it's a bit short of links to back this claim. I guess I might be wrong (I've just never seen this done, but that doesn't strictly mean it doesn't exist...).

As you know, you need a direct connection, or a connection entirely relayed, between the user-agent and the SSL endpoint (in this case, you want it to be Tomcat). This means that Apache Httpd won't be able to look into the URL: it will know the host name at best (when using Server Name Indication).

The only option that doesn't seem to depend on a URL in the mod_proxy documentation is AllowCONNECT, which is what's used for forward proxy servers for HTTPS.

Even the options in mod_proxy_balancer expect a path at some point of the configuration. Its documentation doesn't mention SSL/HTTPS ("It provides load balancing support for HTTP, FTP and AJP13 protocols"), whereas mod_proxy talks at least about SSL when mentioning CONNECT.

I would suggest a couple of options:

• Using an iptables-based load-balancer, without going through Httpd, ending the connections in Tomcat directly.

• Ending the SSL/TLS connection at Httpd and using a plain HTTP reverse proxy to Tomcat.

This second option requires a bit more configuration to deal with the client certificates and Tomcat's security constraints.

If you have configured your webapp with <transport-guarantee>CONFIDENTIAL</transport-guarantee>, you will need to make Tomcat flag the connections as secure, despite the fact it sees them coming from its plain HTTP port. For Tomcat 5, here is an article (originally in French, but the automatic translations isn't too bad) describing how to implement a valve to set isSecure(). (If you're not familiar with valves, they are similar to filters, but operate within Tomcat itself, before the request is propagated to the webapp. They can be configured within Catalina) I think from Tomcat 5.5, the HTTP connector secure option does exactly that, without requiring your own valve. The AJP connector also has a similar option (if using mod_proxy_ajp or mod_jk).

If using the AJP connector, mod_proxy_ajp will forward the first certificate in the chain and make it available within Tomcat (via the normal request attribute). You'll probably need SSLOptions +ExportCertData +StdEnvVars. mod_jk (although deprecated as far as I know) can also forward the entire chain sent by the client (using JkOptions +ForwardSSLCertChain). This can be necessary when using proxy certificates (which are meaningless without the chain up to their end-entity certificate).

If you want to use mod_proxy_http, a trick is to pass the certificate via an HTTP header (mod_header), using something like RequestHeader set X-ClientCert %{SSL_CLIENT_CERT}s. I can't remember the exact details, but it's important to make sure that this header is cleared so that it never comes from the client's browser (who could forge it otherwise). If you need the full chain, you can try out this Httpd patch attempt. This approach would probably need an extra valve/filter to turn the header into the javax.servlet.request.X509Certificate (by parsing the PEM blocks).

A couple of other points that may be of interest:

• If I remember well, you need to download the CRL files explicitly for Httpd and configure it to use them. Depending on the version of Httpd you're using, you may have to restart it to reload the CRLs.
• If you're using re-negotiation to get your client-certificate, a CLIENT-CERT directive will not make Httpd request a client certificate as far as I know (this is otherwise done via a valve that can access the SSLSession when using the JSSE connector directly). You may have to configure the matching path in Httpd to request the client-certificate.