Found this post while looking for the same information. Finally just decided to trial-and-error it, the poor server.

wait 2 seconds
send "username<cr>"
wait 1 seconds
send "password<cr>"

The first wait just ensures it waits long enough for the 'welcome to server' username prompt. The second one is enough for the password prompt to appear.

The wait command seems really powerful is that you could possibly even create IF statements and loops based on what appears at a given point on the screen, ie a "if still showing a progress bar, wait a bit longer before continuing with input", but for this purpose a 'wait for 1 second' will do fine.