Braintree\Configuration::privateKey PHP Méthode

    public static function privateKey($value = null)
    {
        if (empty($value)) {
            return self::$global->getPrivateKey();
        }
        self::$global->setPrivateKey($value);
    }

 /**
  * Bootstrap the application services.
  *
  * @return void
  */
 public function boot()
 {
     \Braintree\Configuration::environment('sandbox');
     \Braintree\Configuration::merchantId(env('BRAINTREE_MERCHANT_ID'));
     \Braintree\Configuration::publicKey(env('BRAINTREE_PUBLIC_KEY'));
     \Braintree\Configuration::privateKey(env('BRAINTREE_PRIVATE_KEY'));
 }