Serving pages from behind a proxy

It depends on kind of WAF. If it’s apache module (as mod_security for example) then you don’t need to change anything.

If it’s reverse proxy then you should replace RewriteCond %{HTTPS} on to RewriteCond %{HTTP:X-Forwarded-Proto} https or RewriteCond %{HTTP:X-Forwarded-Port} 443 but it depends on configuration. If VirtualHost is on custom port then you should also set HTTPS in wp-config.php. More details – https://codex.ww.wp.xz.cn/Administration_Over_SSL#Using_a_Reverse_Proxy

They are server rules (for serving files), but WPSC should create https files and it isn’t possible without changes in wp-config.php because there isn’t place where you can add custom code before loading advanced-cache.php.

So, you need to add similar “rules” in wp-config.php. Something like this:

// in known, safe manner
$trusted_proxies = array( '111.222.233.244', '111.222.233.245' );

if ( ! empty( $_SERVER['REMOTE_ADDR'] ) && in_array( $_SERVER['REMOTE_ADDR'], $trusted_proxies ) ) {
    if ( isset( $_SERVER['HTTP_X_FORWARDED_FOR'] ) ) {
        $ip_addr = explode(',',$_SERVER['HTTP_X_FORWARDED_FOR']);
        $_SERVER['REMOTE_ADDR'] = reset( $ip_addr ); 
	unset( $ip_addr );
    }
    if ($_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https') {
        $_SERVER['HTTPS']='on';
    }
}
unset( $trusted_proxies );

You should add it before comment: /* That’s all, stop editing! Happy blogging. */.

I didn’t test this code, but it’s concept. Related to rewrite rules, it’s possible to use mod_setenvif module to set environment variable which could be used later (to avoid repeating same rules which isn’t perfect for performance).

There is an issue on github – https://github.com/Automattic/wp-super-cache/issues/634 related to optimization of rewrite rules. Probably you could use something like this.

It’s possible only with custom PHP script. You need to upload it into root directory (where is index.php,wp-load.php) and execute it in browser (https://example.com/cdn-update.php).

Script:

<?php

// Load the WordPress library.
require_once( dirname(__FILE__) . '/wp-load.php' );

foreach( get_sites( array( 'public' => 1 ) ) as $site ) {
        update_blog_option( $site->blog_id, 'ossdl_off_cdn_url', 'https://cdn.example.com/' );
}

I hope that you have basic PHP knowledge and you can even get option, replace URL and update it.

It’s possible that some plugin was stuck in bootstrap process. You can add following constants before wp-load.php:

define( 'DOING_AJAX', true );
define( 'WP_USE_THEMES', false );
define( 'SHORTINIT', true );

It stops bootstrap process after multisite init and you can’t use entire WP API (and WPSC isn’t fully loaded), but get_sites and update_blog_option should work.

Also, if you have shell access then you can run it as shell command. Something like this:

cd public_html
php cdn-update.php

In this case you should set virtual $_SERVER global (before wp-load.php). Also, it’s possible that you need to run php-cli instead of php. Example:

$_SERVER = array(
  "HTTP_HOST"      => "example.com",
  "SERVER_NAME"    => "example.com",
  "SERVER_PORT"    => 443,
  "REQUEST_URI"    => "/",
  "REQUEST_METHOD" => "POST",
);

Also, it’s possible to move these scripts outside public_html to protect them. I’m running various cron jobs via php-cli (custom preload, backup,…).