Hi Mitch,
When I first added the SSL stuff, not passing a certificate and key worked. I haven't tested this for a while, and it seems the CL+SSL version you are using somehow doesn't support it. All Postmodern does is call (make-ssl-stream socket :key *ssl-key-file* :certificate *ssl-certificate-file*) -- see cl-postgres/protocol.lisp.
Best, Marijn