controlador-descarga/components/rest/JsonController.php

<?php

namespace app\components\rest;

use yii\filters\ContentNegotiator;
use yii\filters\Cors;
use yii\filters\VerbFilter;
use yii\rest\Controller;
use yii\web\Response;

class JsonController extends Controller {

  public $serializer = 'app\components\rest\Serializer';

  public function behaviors() {
    $behavior = parent::behaviors();
    $behavior['contentNegotiator'] =  [
      'class' => ContentNegotiator::className(),
      'formats' => [
        'application/json' => Response::FORMAT_JSON,
        'application/xml' => Response::FORMAT_XML,
      ],
    ];
    $behavior['corsFilter'] = [
      'class' => Cors::className(),
      'cors' => [
        'Origin' => ['*'],
        'Access-Control-Request-Method' => [
          'GET', 'POST', 'PUT', 'PATCH', 
          'DELETE', 'HEAD', 'OPTIONS'
        ],
        'Access-Control-Request-Headers' => ['*'],
      ],
    ];
    $behavior["authenticator"]["except"] = ['options'];
    return $behavior;
  }

  public function beforeAction($action) {
    if (!parent::beforeAction($action)) return false;
    \Yii::$app->getResponse()->format = Response::FORMAT_JSON;
    return true;
  }

}