It is not exactly easy to add a new user to Nagios but this is how it can be done.
If using ubuntu you will need to modify /usr/local/nagios/etc/cgi.cfg
The important one to view the information on the web interface is “authorized_for_system_information”. It should look like this if you are adding multiple users.
There are more fields that you can use. These are all the categories that nagiosadmin (the default account) is in.
authorized_for_configuration_information authorized_for_system_commands authorized_for_all_services authorized_for_all_hosts authorized_for_all_service_commands
Alternatively you can set a variable so you can add a user to all groups from one line. You can add this to the top of the cgi.cfg file.
$users = nagiosadmin,cbrown,jcutright
Then change each to use the variable.
authorized_for_configuration_information=$users authorized_for_system_commands=$users authorized_for_all_services=$users authorized_for_all_hosts=$users authorized_for_all_service_commands=$users
Once you have added the user to all or any of these sections you will need to add the user the htpasswd.
htpasswd /usr/local/nagios/etc/htpasswd.users jcutright
Now just restart Apache and Nagios and you should be good to go.
service apache2 restart service nagios restart