How to only allow URLs with specific parameter in Apache?

I using Piwik to track my websites visitors. As a matter of "security" I only allow the access to index.php a few known IPs. My problem is that the Piwik opt-out snippet is only available via this index.php.

I tried to solve this via RewriteRule's and Location/Files directives but I won't able to allow only the specific URL parameter and let others deny.

For all those people who don't know (much) Piwik but Apache here a the basic points:

• The administrative GUI is available via index.php which it's access is limited to known IPs.
• The Piwik opt-out snippet is only available via index.php with a known parameter set: index.php?module=CoreAdminHome&action=optOut&lang=DE

What I want is:

• Deny access to index.php from all unknown IPs but known IPs. (done)
• Allow access to the opt-out parameter set for index.php from all IPs. (pending)

How to only allow URLs with specific parameter in Apache?

I tried:

Order allow,deny Allow from all <Files "index.php"> Order allow,deny Deny from all Allow from 127.0.0.1 </Files> RewriteEngine On RewriteRule ^/piwik-opt-out.html$ index.php?module=CoreAdminHome&action=optOut [L] <Location "/piwik-opt-out.html"> Order allow,deny Allow from all </Location>