Laravel 9 Error: Undefined constant Illuminate\Http\Request::HEADER_X_FORWARDED_ALL

Solve the error when upgrading the system to laravel 9 or 10. "Undefined constant Illuminate\Http\Request::HEADER_X_FORWARDED_ALL"

Reason: 

As of Laravel 9, the framework switched to using a built-in middleware to handle proxy queries instead of Fideloper\Proxy\TrustProxies. So when upgrading from lower versions like laravel 5.8, laravel 8 to laravel 9 we also need to edit to replace this middleware. If you don't make changes you will get an error when you run "composer update" and you won't be able to access the website

Solve the problem:

Step 1: Edit your current TrustProxies Middleware (app/Http/Middleware/TrustProxies.php)

Step 2: Update middleware according to the following example

<?php
namespace App\Http\Middleware;
use Illuminate\Http\Middleware\TrustProxies as Middleware;
use Illuminate\Http\Request;
class TrustProxies extends Middleware
{
    /**
     * The trusted proxies for this application.
     *
     * @var array<int, string>|string|null
     */
    protected $proxies;
    /**
     * The headers that should be used to detect proxies.
     *
     * @var int
     */
    // Before...
    // protected $headers = Request::HEADER_X_FORWARDED_ALL;
    // After...
    protected $headers =
        Request::HEADER_X_FORWARDED_FOR |
        Request::HEADER_X_FORWARDED_HOST |
        Request::HEADER_X_FORWARDED_PORT |
        Request::HEADER_X_FORWARDED_PROTO |
        Request::HEADER_X_FORWARDED_AWS_ELB;
}

Step 3: Remove Fideloper TrustProxies from composer file

composer remove fideloper/proxy

Step 4: Done ! run "composer update" to complete update