code: private function pair($segment)
      {
          $segmentPattern = '/\A(keyId|algorithm|headers|signature)="(.*)"\z/';
          $matches = [];
          $result = preg_match($segmentPattern, $segment, $matches);
          if (1 !== $result) {
              throw new SignatureParseException("Signature parameters segment '$segment' invalid");
          }
          array_shift($matches);
  
          return $matches;
      }
docs: @param $segment
  
  @return array
  
  @throws SignatureParseException