I'm not able to cache my PHP rewritten CSS file - php

Question

I have a php file that is renamed in htaccess as a css file. The reason being, is because I have some styles and colors which change based on some admin options.
Anyway, I am trying to allow a visitor's browser to cache the file. Here's what I have:
style.php:
header("Content-type: text/css; charset: UTF-8");
// Start normal CSS styles...
.htaccess:
RewriteRule ^assets/css/min/([a-zA-Z0-9\._-]+)/([a-zA-Z0-9\._-]+)/([a-zA-Z0-9\._-]+)\.css$ assets/css/min.php?style=$1&layout=$2&ver=$3 [L,QSA]
# Compress
AddOutputFilterByType DEFLATE text/css
# Cache for 1 week
<FilesMatch ".(css)$">
Header set Cache-Control "max-age=604800"
</FilesMatch>
<IfModule mod_expires.c>
ExpiresActive on
ExpiresByType text/css "access plus 1 week"
</IfModule>
In the page head:
<link rel="stylesheet" href="http://example.com/assets/css/min/blue/flat/0.9.2.css">
Each time a new page is loaded, the page contents are requested. These are the headers I receive:
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Connection: Keep-Alive
Content-Encoding: gzip
Content-Length: 13881
Content-Type: text/css; charset: UTF-8;charset=UTF-8
Date: Sat, 20 Feb 2016 22:49:17 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Keep-Alive: timeout=5, max=94
Pragma: no-cache
Server: Apache/2.4.16 (Unix) OpenSSL/1.0.1p PHP/5.6.12 mod_perl/2.0.8-dev Perl/v5.16.3
Vary: Accept-Encoding,User-Agent
X-Powered-By: PHP/5.6.12

Answer 1

Your mod_expires config applies to files based on their mimetype as perceived by the webserver. Unless you've done some major surgery on the webserver config elsewhere, the webserver will not associate the text/CSS mimetype with files ending in .php (and if it did, much further hacking would be required to get them processed by the PHP parser). The header set by your PHP script is irrelevant to this process.
While it is possible to force mod_expires to add caching headers to the response, you'll also have to use mod_headers to remove the values PHP sets; when a browsers receives multiple conflicting caching instructions, it will resort to the shortest expiry time expressed in them.
Hence, to make the content cacheable, you should emit the caching information directly from the PHP script. E.g.
header('Cache-control: max-age=604800; private');
But basing the expiry time on the access time is not the best solution.