protected function addPrefixedHeaders(RequestInterface $request, Parameter $param, $value)
    {
        if (!is_array($value)) {
            throw new InvalidArgumentException('An array of mapped headers expected, but received a single value');
        }
        $prefix = $param->getSentAs();
        foreach ($value as $headerName => $headerValue) {
            $request->setHeader($prefix . $headerName, $headerValue);
        }
    }