Strange behaviour with apache2

[Alan Chandler <alan@chandlerfamily.org.uk>]

I have a really strange situation with apache2 and the way it is running a php 
file in some circumstances and offering it up to the browser as text in 
others.  The file in question is index.php as the key file using the drupal 
content management system.

I have authentication set on most directories in my server configuration so 
that if I access the web server from outside it requires authentication.  If 
it is from a machine running on the local network it doesn't.  The 
configuration is thus

Alias /drupal /usr/share/drupal

<Directory /usr/share/drupal/>
        Options +FollowSymLinks
        AllowOverride All
        #
        # Controls who can get stuff from this server.
        #
        AuthType Basic
        AuthName "Chandler Intranet"
        AuthUserFile /etc/apache2/users
        AuthGroupFile /etc/apache2/groups
        Require group family
        Order allow,deny
        Allow from 192.168.0.0/24
        Satisfy any
</Directory>

The .htaccess file has (amongst other things) 

DirectoryIndex index.php

in it, and so in fact does the main server configuration.

When I access the web server with the url http://myserver/drupal from a 
192.168.0.0/24 address, it works and index.php gets executed as a php script.  

When I access this url from outside I get prompted for a user name and 
password which I enter correctly and then find that the text of index.php not 
sent as html (at least I am prompted by Internet Exlorer to either save or 
open the file.  When I choose wordpad, I have recieved the text inside 
index.php)

Just to convince myself that php can really run, I have another directory 
phptest with an index.php file as follows

<?php phpinfo(); ?>

and when I call this up (http://myserver/phptest ) from outside I get a 
detailed web page full of php information.

I just cannot think what it could be about my apache configuration that 
changes the behaviour dependant on the source of the browser. 

Anyone any ideas?

Or ... any ideas about I can understand how exactly the apache configuration 
file has been parsed so that I can locate the source of my problem. 

















-- 
Alan Chandler
alan@chandlerfamily.org.uk
First they ignore you, then they laugh at you,
 then they fight you, then you win. --Gandhi