/etc/nagios3/debian-edu/htpasswd.users is in debian-edu-config 1.818+deb8u2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1
nagiosadmin:$1$zzYXNMkf$KM0cGbMKb/TXJxbLWu7RX0