@SuppressWarnings("unchecked")
    public static Map<String, String> getAppEngineHeaders(HttpServletRequest req)
    {
        Map<String, String> headers = new HashMap<String, String>();
        for(Enumeration<String> en = req.getHeaderNames(); en.hasMoreElements();)
        {
            String key = en.nextElement();
            String val = req.getHeader(key);
            if(!key.startsWith("X-AppEngine-"))
                continue;
            headers.put(key.substring("X-AppEngine-".length()), val);
        }
        return headers;
    }