i wanna have authentication for nagios .
i set use authentication option to 1 in cgi.cfg and create .htaccess in both share/ and sbin/ subdirectories .
i also used ’ htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin ’ to set password for nagiosadmin user .
now i have been asked for entering usrname ans passwd for accessing the nagios on server. but when i enter nagiosadmin and passwd it asks me again for entering them .
why is it so ?
follow all the instructions about authentication and check them again to be sre you didi it correctly. 
Quite easy you mised a step.
Luca
I recently had a heck of a time with getting a fresh nagios install on CentOS to work. I had your problem until I uninstalled mod_auth_mysql.
Apache kept complaing about user “whoever” not found in mysql db. Well, of course, I want the users in the text file /usr/local/nagios/etc/htpasswd.users
tnx friends,
the problem is solved now,
i have changed the permissions of htpasswd.users and it works well.
It might help someone to know what the permissions where and what they are now. Just for reference.