I built Nagios 3.2.0 on a CentOS v5 server with Apache 2. The file /sample-config/httpd.conf that was created by the build process has a syntax error that is causing errors during Nagios web authentication (error message: "you are not authorized to access /nagios on this server") and in /var/log/httpd/error_log (error message: "Directory index forbidden by Options directive"). The httpd.conf file that was created has a line of the form:
Alias /nagios/ "/opt/nagios/share"
The Apache HTTP server version 2 documentation states that if the alias value ends in a / then the directory value must also end in a /. I checked my nagios 3.0.6 build directory, and the sample-config/httpd.conf file was created with the correct syntax (no ending slash on either value).
The Nagios 3.2.0 code that I used was download from www.nagios.org and was dated 2009-08-12