hosts.allow: %u not working (log username)

I need to keep track of all SSH connections on my server. In my /etc/hosts.allow I have something like this: sshd: ALL : spawn ( echo "date from %u %a " >> /var/log/ssh/%d.log ) & where %a logs the client IP, and %u is supposed to log the username. But instead %u just logs unknown. Is there a way to fix this? I need to log both the IP and the username for each connection.