code: public void sendChallenge(UserRealm realm,
                                HttpRequest request,
                                HttpResponse response,
                                boolean stale)
          throws IOException
      {
          response.setField(HttpFields.__WwwAuthenticate,
  			    "Digest realm=\""+realm.getName()+
  			    "\", domain=\""+
  			    response.getHttpContext().getContextPath() +
  			    "\", nonce=\""+newNonce(request)+
  			    "\", algorithm=MD5, qop=\"auth\"" + (useStale?(" stale="+stale):"")
                            );
          
          response.sendError(HttpResponse.__401_Unauthorized);
      }
docs: /* ------------------------------------------------------------