How to use constants with Request in Laravel5

I am trying to upgrade my Laravel4 app to Laravel5.

In my Laravel4 app, I use app/config/constants.php file and difine constants by using Request class.

if (Request::is('admin/*'))
{
    define('PATH', 'admin')
}else
{
    define('PATH', 'public')
}

and read it in app/start.php.

require __DIR__.'/../app/config/constants.php';

These constants are used in controllers, models, commands, views, and files in 'app/config' directory.

In Laravel5, how to read this file?

I tried: 1, added it in config directory and changed composer.json

"autoload": {
    "files": [
        "config/constants.php"
    ]
}

I got error: PHP Fatal error: Class 'Request' not found

2, added it in config directory and changed app/Providers/AppServiceProvider.php

public function boot()
{
    require __DIR__.'/../config/constants.php';
}

I got same error: PHP Fatal error: Class 'Request' not found

Thanks,

via Chebli Mohamed