code: protected function normalizeProxyHeader( $header )
      {
          $header = strtoupper( $header );
          $header = str_replace( '-', '_', $header );
          if ( 0 !== strpos( $header, 'HTTP_' ) )
          {
              $header = 'HTTP_' . $header;
          }
          return $header;
      }
docs: Normalize a header string
  
  Normalizes a header string to a format that is compatible with
  $_SERVER
  
  @param  string $header
  @return string