Understanding Redirects

I have a WordPress website that is working well. The website is shared hosted on a popular hosting site. It was migrated/transferred from a different hosting site to the current one (this point is mentioned as it may play a role in the answer to these two questions). The site has an SSL on the existing site and also had one the original site. I have changed the name servers at the domain registrar to point to the new hosting site.

If Modified Since HTTP Header

I am trying to enable 304 If Modified Since HTTP header in my WordPress site. After doing lot of Googling I find out a site where the author said to put the following line at the very end of wordpress wp-config.php file. Here is the line of code:

How do I use the ‘http_request_host_is_external’ filter

I’m having a really hard time trying to use the http_request_host_is_external filter. For some background, I’m trying to set up a separate server to handle private plugin and theme updates. The problem is that it’s on a separate server, so the WordPress wp_http_validate_url (wp-includes/http.php) function kills the request. The following are lines 481-503 of that file.