Question

How do I configure PHP and nginx to display errors only for specific IP addresses?

Answer 1

You could first set PHP to not display errors at all (display_errors = Off in php.ini), then use the auto_prepend_file directive in your php.ini to include this script:

<?php
$allowed_ips = array('111.111.111.111', ...);
if (in_array($_SERVER['REMOTE_ADDR'], $allowed_ips)) {
    ini_set('display_errors', '1');
}