is normally only necessary if the webserver is behind a proxy which does terminate TLS.
In this case, the original IP address is usually forwarded to the backend server as an additional HTTP Request Header.
This could be either X-Forwarded-For, RFC 7239 compliant Forwarded or any other Non-Standard-Header.
You'll have to find out which header is being used and (ideally) configure your webserver acordingly (eg. by using mod_rpaf/mod_remoteip for Apache, ngx_http_realip_module for nginx).