Password Authentication for Below Directories
The next step is to create a file named .htaccess in the root your CGI directory (and optionally also you HTML directory) for Nagios (usually /usr/local/nagios/sbin and /usr/local/nagios/share, respectively). The file(s) should have contents similiar to the following...
AuthName "Nagios Access"
Now to create the Users
# htpasswd -c /usr/local/nagios/etc/htpasswd.users nagiosadmin
Re-type new password:
Adding password for user nagiosadmin
Password I added as admin
Okay, so you're done with this part of what needs to be done. If you point your web browser to your Nagios CGIs you should be asked for a username and password. If you have problems getting user authentication to work at this point, read your webserver documentation for more info.
Once you've finished editing the Apache configuration file, you'll need to restart the web server with a command like this...
Verify Your Changes
Don't forget to check and see if the changes you made to Apache work. You should be able to point your web browser at http://yourmachine/nagios and get the web interface for Nagios.
To Troubleshoot any errors on Apache Server Check the logs
#tail -f /var/log/httpd/error_log