maximum entropy <entropy@entropy.homeip.net> output:
:4.  $ ssh-keygen -t dsa -N "" -f $HOME/.ssh/id_dsa

I think this is why it didn't work for me.  I wasn't using one of
(excerpt from src/lib/libpam/modules/pam_ssh/pam_ssh.c:79)
	static const char *pam_ssh_keyfiles[] = {
        	".ssh/identity",        /* SSH1 RSA key */
		".ssh/id_rsa",          /* SSH2 RSA key */
		".ssh/id_dsa",          /* SSH2 DSA key */
		NULL
	};

I'm guessing that these are allowed in addition to authorized_keys.
Although I haven't confirmed it, I can't think of any other reason
why they are in the pam_ssh.c file.  In fact, pam_ssh(8) mentions
them but doesn't mention why.

Regards,
Geoff