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.
authorized_for_system_information=nagiosadmin,cbrown,jcutright
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