You can use mod_ssl with basic auth to allow only who have presented a valid certificate. You need to modify the LimitExcept part like this:
AuthName "no-GET thingy"
if it's in Apache's environment, you have to get it from Apache. In other words, a job running under the Apache process should be able to access and return the value - in other words a CGI script or other dynamic web content.
For example with PHP you might get it by writing the following to lynx.php in the webroot then browsing to http://server/lynx.php (...