found how to do this under an xbmc thread somewhere.
for simplicity, download shairport, compile it, and move the folder to ~/yourusername/.shairport
Find the line (52) where it starts with “my $hairtunes_cli =” change the path to the hairtunes file in the shairport folder
sudo nano shairport.pl
Find the line (20) where it starts with “DAEMON =” change the path to the shairport.pl file in the shairport folder
sudo cp shairport.init.sample /etc/init.d/shairport
sudo nano /etc/init.d/shairport
Test, then reboot and test!
sudo chmod +x /etc/init.d/shairport
sudo update-rc.d shairport defaults
sudo service shairport start
i literally just stumbled on this now and knew there was a thread here with no response that ive stumbled on many times looking for an answer myself!
after re-reading your thread i cant comment on the login issue though... but this will certainly run it as a service.