Yii2 Modfied Web Application to Redirect to Https under a Load Balancer provided by AWS.

MyWebApplication.php

<?php

namespace common\components;

use Yii;
use yii\web\Application;

/**
 * Reescribo para siempre usar HTTPS si es que la url no es segura
 * Class MyWebApplication
 * @package common\components
 */
class MyWebApplication extends Application
{
    public function handleRequest($request)
    {
        //Si la conexión no es segura, y no está en localhost cambiamos la url para usar SSL
        if (!$this->isSecuredByAWS() && !$this->isLocalhost() && !$this->isHealthCheck()) {
            //otherwise redirect to same url with https
            $secureUrl = str_replace('http', 'https', $request->absoluteUrl);
            //use 301 for a permanent redirect
            return Yii::$app->getResponse()->redirect($secureUrl, 301);
        } else {
            //if secure connection call parent implementation
            return parent::handleRequest($request);
        }
    }

    /**
     * Al estar detrás de un balanceador de carga no sabemos el protocolo,
     * sin embargo AWS agrega como header HTTP_X_FORWARDED_PROTO
     */
    function isSecuredByAWS()
    {
        //Si el header está, y es https quiere decir que está asegurado a través de un balanceador de carga
        if (!empty($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] == "https") {
            return true;
        } else {
            return false;
        }
    }

    /**
     * Retornamos true si estamos en localhost
     * @return bool
     */
    function isLocalhost()
    {
        return $_SERVER['SERVER_NAME'] == 'localhost' ;
    }

    function isHealthCheck()
    {
        return $_SERVER['REQUEST_URI'] == '/health-check' ;
    }
}