I will like to do this request in the browser: https://file.domain.com/iums50.js But Im really doing a request for the page: https://file.domain.com/get.php?f=iums50.js I don't want to redirect the user, I will like to put the content of get.php?f=iums50.js in https://file.domain.com/iums50.js, using .htaccess
Look into htaccess proxies ([P] flag). Set the HTTP_HOST in the RewriteCond to ^file\.domain\.com$ and insert get.php?f= into the link in the RewriteRule.