Httpd – Adding missing header in Apache HTTP response

Try using the SetEnvIf directive, coupled with env in your Header directive:

SetEnvIf Request_URI "/MyCGI" is_cgi
Header set X-Frame-Options some-value env=!is_cgi

(or something close to that :-))

In the past I have used a intermediate VirtualHost entry as a work-around for similar situations when certain directives didn't play well together:

Your current configuration may look like:

<VirtualHost *:80>
   ServerName www.example.com
   ProxyPass /app http://app.example.com/app
   ProxyPassReverse /app http://app.example.com/app
</VirtualHost>

Modify that to point to the intermediate virtual host and strip your header from the responses:

<VirtualHost *:80>
   ServerName www.example.com
   ProxyPass /app http://localhost:8000/app
   ProxyPassReverse /app http://localhost:8000/app
   Header unset Cast
</VirtualHost>

and a new virtual host where you can still log your Cast headers:

Listen 127.0.0.1:8000
<VirtualHost 127.0.0.1:8000>
   ServerName localhost
   ProxyPass /app http://app.example.com/app
   ProxyPassReverse /app http://app.example.com/appp
   LogFormat %{X-Forwarded-For}o %{Cast}o ...
</VirtualHost>