Custom wp-config for wordpress behind reverse proxy & using a staging server

wp-config.php

/* Staging and reverse proxy settings */

$public_url         = 'https://public-server.com';
$production_server     = 'production.example.com';
$staging_server     = 'stage.example.com';

/* Staging and reverse proxy code */

if($_SERVER['REQUEST_URI'] == "/?cookiesetter"){

    setcookie("admincookie", 'exists', time()+3600*6, '/', $production_server, true, true);  /* expire in 6 hours */
    header("Location: https://$production_server/wp-admin/", TRUE, 302);
    exit;

}

if($_SERVER['REQUEST_URI'] == "/?cookieremover"){

    setcookie("admincookie", '', time()-3600, '/', $production_server, true, true);   /* expired, removes cookie */
    header("Location: /", TRUE, 302);
    exit;

}

if($_SERVER['HTTP_HOST'] == 'staging_server'){
    
    define( 'WP_SITEURL', "https://$staging_server" );
    define( 'WP_HOME', "https://$staging_server" );

    header("X-Robots-Tag: noindex, nofollow", true);

}

if($_SERVER['HTTP_HOST'] != $staging_server ){
    
    if(isset($_COOKIE['admincookie'])){
            
        define( 'WP_SITEURL', "https://$production_server" );
        define( 'WP_HOME', "https://$production_server" );
        
    } else {

        define( 'WP_SITEURL', "https://$production_server" );
        define( 'WP_HOME', $public_url );
    }

}