code: public function getTokenFromServer()
      {
          $params = [
              'appid' => $this->appId,
              'secret' => $this->secret,
              'grant_type' => 'client_credential',
          ];
  
          $http = $this->getHttp();
  
          $token = $http->parseJSON($http->get(self::API_TOKEN_GET, $params));
  
          if (empty($token[$this->tokenJsonKey])) {
              throw new HttpException('Request AccessToken fail. response: '.json_encode($token, JSON_UNESCAPED_UNICODE));
          }
  
          return $token;
      }
docs: Get the access token from WeChat server.
  
  @throws \EasyWeChat\Core\Exceptions\HttpException
  
  @return string