code: public function createAbsoluteUrl($params, $scheme = null)
      {
          $params = (array) $params;
          $url = $this->createUrl($params);
          if (strpos($url, '://') === false) {
              $url = $this->getHostInfo() . $url;
          }
          if (is_string($scheme) && ($pos = strpos($url, '://')) !== false) {
              $url = $scheme . substr($url, $pos);
          }
  
          return $url;
      }
docs: Creates an absolute URL using the given route and query parameters.
  
  This method prepends the URL created by [[createUrl()]] with the [[hostInfo]].
  
  Note that unlike [[\yii\helpers\Url::toRoute()]], this method always treats the given route
  as an absolute route.
  
  @param string|array $params use a string to represent a route (e.g. `site/index`),
  or an array to represent a route with query parameters (e.g. `['site/index', 'param1' => 'value1']`).
  @param string $scheme the scheme to use for the url (either `http` or `https`). If not specified
  the scheme of the current request will be used.
  @return string the created URL
  @see createUrl()