Question

I am trying to make a Tomcat web application use client certificate authentication for incoming connections. Everything works fine when using clientAuth=true in server.xml, however due to other applications running on the same server, we cannot use this in the production environment.

Is there a way to form a web.xml document such that it forces client certificate usage for the application in the same way as clientAuth=true? It seems like using the CLIENT-CERT setting also requires you to setup a tomcat user account for each certificate which is to access your system? We need to be able to allow all certificates which are from a specified CA (set in the server truststore) where the subject matches certain rules (checked within the actual application). I was hoping that something like the following would work, but no luck yet!

<security-constraint>
    <web-resource-collection>
        <web-resource-name>Everything</web-resource-name>
        <url-pattern>/*</url-pattern>
    </web-resource-collection>
    <user-data-constraint>
        <transport-guarantee>CONFIDENTIAL</transport-guarantee>
    </user-data-constraint>
</security-constraint>
<login-config>
    <auth-method>CLIENT-CERT</auth-method>
</login-config>

Answer 1

First of all, it sounds like you want clientAuth=want instead of clientAuth=true: that will allow the client to provide a certificate but not absolutely require one.

When you use authentication of any kind, Tomcat (or any servlet container for that matter) must be able to build a Principal object out of it — one that has a name (usually a username). The container then must decide what roles the user has in order to properly authorize a particular request. So, Tomcat will need to know about the users beforehand in order to make authorization work.

On the other hand, if you don’t need any authorization, you could set clientAuth=want and then use a Filter to verify the certificate. There’s no need to use CLIENT-CERT authentication if you are already doing your own checking.