code: protected function getSignContent(array $toBeSigned, $verify = false)
      {
          ksort($toBeSigned);
          $stringToBeSigned = '';
          foreach ($toBeSigned as $k => $v) {
              if ($v !== '') {
                  if ($verify && $k != 'sign' && $k != 'sign_type') {
                      $stringToBeSigned .= $k . '=' . $v . '&';
                  }
                  if (!$verify && $v !== '' && !is_null($v) && $k != 'sign' && '@' != substr($v, 0, 1)) {
                      $stringToBeSigned .= $k . '=' . $v . '&';
                  }
              }
          }
          $stringToBeSigned = substr($stringToBeSigned, 0, -1);
          unset($k, $v);
          return $stringToBeSigned;
      }
docs: 数据签名处理
  @param array $toBeSigned
  @param bool $verify
  @return bool|string