PHP $_SERVER('REQUEST_URI') Showing Unexpected Result (httpd.conf, ssl) - php

Question

NOTE: I am not the system admin, so my knowledge and ability to edit system config files is somewhat limited.
A server that recently went all-Https was not displaying our 404 page like it was before the switch.
Not Found
The requested URL /toh was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to
use an ErrorDocument to handle the request.
In our httpd.conf page, we had the line
ErrorDocument 404 /admin/404/
When we changed this line to
ErrorDocument 404 https://example.com/admin/404/
everything seemed to work fine; the Not Found error went away and the 404 page was properly displayed.
However,
This 404 page detects where the user was originally coming from using
$_SERVER['REQUEST_URI'];
The page would then check a database, see if that URI was in there, and would then redirect the client to the appropriate page.
So, for example, if the user came to the page from:
http://example.com/tacos
In the event that wasn't a valid link, the 404 page would see the /tacos link, find it in a database, and redirect the user where he/she needed to go.
Now, the $_SERVER['REQUEST_URI'] only spits out
/admin/404
regardless of where the user was coming from.

Answer 1

So apparently the problem was twofold:
1) Per this thread here, the ErrorDocument link must not have the domain name; it must be in the format
ErrorDocument 404 /admin/404
2) In the .conf file, the did not have the RewriteEngine turned on; it was commented out. So we uncommented the following rules
<VirtualHost 127.0.0.1:80>
...
# RewriteEngine on
# RewriteCond %{HTTP_HOST} ^example\.com [NC]
# RewriteCond %{REQUEST_URI} /$ [NC]
# RewriteRule ^(.*)/$ https://www.example.com/$1 [L,R=301]
...
RedirectMatch permanent ^(.*)/$ https://www.example.com/$1
</VirtualHost>
Now, the 404 page is found and $_SERVER(['REQUEST_URI']) has the appropriate resource.