This description is valid for Nagios 3.

In situations, where you cannot use send_nsca for submitting passive check results over the network, you can use the Nagios web interface. You need an http account

• Allowed to access nagios by your webserver, normally accomplished with Basic Auth and htpasswd.
• Allowed to submit passive check results via cgi, this can be done either by
  • via dedicated permissions on the host(s) and service(s) in question
    

or

• Allowed to view all services/hosts¹⁾ via /etc/nagios3/cgi.cfg
• Allowed to submit commands for all services/hosts²⁾ via /etc/nagios3/cgi.cfg

At least if you are going to use dedicated permissions, you need to define a nagios contact, that might look like:

define contact{
        contact_name                    passive_via_http
        alias                           passive_via_http
        service_notification_period     never
        host_notification_period        never
        service_notification_options    n
        host_notification_options       n
        service_notification_commands   notify-service-by-email
        host_notification_commands      notify-host-by-email
      }

Assuming you have your credentionals for the account http_remote saved in either ~/.wgetrc or ~/.netrc, this example will submit a passive check result for the service TEST on host localhost in status UNKNOWN³⁾:

wget -O - \
     --user=http_remote \
     --auth-no-challenge \
     --no-check-cert \
'https://<nagios-server>/cgi-bin/nagios3/cmd.cgi'\
'?cmd_typ=30'\
'&cmd_mod=2'\
'&host=localhost'\
'&service=TEST'\
'&plugin_state=3'\
'&plugin_output=Test+mit+wget+II'\
'&btnSubmit=Commit'

Of course, in a large environment with appropriate security needs, you would write a PHP script that is restricted to write passive checks.