squid cert test

I have a HTTPS server that expects the client to provide a certificate. This cert uses a passphrase. Everything works fine. But if I use SQUID as my proxy then the authentication fails and squid returns a 503.

Is there anything special I would need to configure in squid? I couldn't find anything in the docs.

I'm getting the following in the squid cache.log

fwdNegotiateSSL: Error negotiating SSL connection on FD 15: error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure (1/0/0)
-- EDIT--

Well, I found the configuration I needed to add and now it's working as expected:

sslpassword_program /etc/squid/program.sh
sslproxy_client_key /etc/squid/keys/cert.pem
I put my cert.pem into the /keys folder. Then program.sh is a very simple program that prints the passphrase. This is all it has:

#!/bin/sh
echo "mypassphrase"
Restarted squid and now it's working!