Is ist possible to get the HTTP headers from a Portlet? According to the docs PortletRequest it should be possible to get the headers using the getProperty method:

A portlet can access portal/portlet-container specific properties through this method and, if available, the headers of the HTTP client request.

headers=req.getPropertyNames();
 while(headers.hasMoreElements()){
 String header= (String) headers.nextElement();
 log.info(header);
 }