Comment # 3 on bug 954273 from Diego Ercolani

Sorry, was my fault... there was another configuration file where there was 
"Require all granted" on the same direcoties... that's why there was no need of
authentication from apache2 point of view.

The only problem is that mod_info don't seem to show all the running
configuration directives... very useless!

Comment # 2 on bug 954273 from Diego Ercolani

Created attachment 655213 [details]
working /etc/apache2/conf.d/nagios.conf

Finlly I found a recipe to make things working: it seem that Under "Directory"
tag isn't possible to use http authentication infact I addedd 2 "location"
sections where authentication seem to work.
It seem also the "and" tag <RequireAll> don't work as expected....

I think theri is a major issue with this apache2 version....