Make a backup of the configuration file you are editing before making modifications to any PAM configuration files.

The following sshd will prompt users who ssh to a Unix machine first for a password, then prompt for a two factor SecurID authentication:

#%PAM-1.0
auth       required     pam_stack.so service=system-auth
auth       required     pam_securid.so
auth       required     pam_nologin.so
account    required     pam_stack.so service=system-auth
password   required     pam_stack.so service=system-auth
session    required     pam_stack.so service=system-auth
session    required     pam_loginuid.so

If you are not receiving a passcode prompt for the second authentication prompt, check the /etc/ssh/sshd_config file and ensure the ChallengeResponseAuthentication parameter is set to yes, as in the example below:

ChallengeResponseAuthentication yes

If it is not set to yes, make the change and then restart ssh as root:

service sshd restart

#%PAM-1.0
auth       required     pam_securetty.so
auth       required     pam_stack.so service=system-auth
auth       required     pam_nologin.so
auth       required     pam_securid.so
account    required     pam_stack.so service=system-auth
password   required     pam_stack.so service=system-auth
# pam_selinux.so close should be the first session rule
session    required     pam_selinux.so close
session    required     pam_stack.so service=system-auth
session    required     pam_loginuid.so
session    optional     pam_console.so
# pam_selinux.so open should be the last session rule
session    required     pam_selinux.so open