How to create REDIRECT_URL?

Question

Nginx

I communicate with the developer of one of the modules for CMS.
In the correspondence he writes:

Perhaps the following fields are missing in the SERVER parameter in php:
HTTP_HOST
REDIRECT_URL
REQUEST_URI
They must be added in the server settings.

Output: empty. Servers on NGINX. How to create REDIRECT_URL? And what should this setting be?
echo $_SERVER['REDIRECT_URL'];

Answer 1

To begin with, write down the essence in more detail.
What do you want to implement? , the user visits http://mysite , he is redirected from the root directory ?