Apache Alias for all domains on the server - custom autodiscover file

I'm trying to set up a custom alias for all domains on the server - a custom autodiscover setup, so that for all domains, the path "/autodiscover/autodiscover.xml" is sent to a file on the server "/home/ruonline/public_html/autodiscover.php" This is exactly the question asked in the link below, but the answer is unclear, and the link in the discussion is dead.