Custom 400 error for client-certificate-authenticated site

Hi everyone,

I'm using nginx as a Proxy SSL front-end for an application, to encapsulate the security features that the application lacks. The site has to authenticate users with a personal certificate. Everything works fine, execpt the case when the user doesn't send the client certificate. In that case a 400 error is generated with the message "No required SSL certificate was sent". But I cannot change the standard page because the site requires the client certificate.

Any idea on how to do this?

Regards