PHP判斷客戶端協議類型是否爲https

PHP官方建議方法：

  if (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off') {
      echo "是https協議";
  }

帶轉發的情況下：

$protocol = ((isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on') || 
                     (isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https')) ? 'https : 'http';