String GetIdentity(const Renderer *r)
{
	// This ugly hack expects that __identity__ is always present in r->var
	Http *http = const_cast<Http *>(dynamic_cast<const Http *>(r));
	if(!http)
		throw Exc("invalid POST identity call");
	Value val = http->var[0];
	String s;
	if(IsString(val))
	{
		s = http->var[0];
		if(s.GetCount())
			return s;
	}
	s = AsString(Uuid::Create());
	http->SessionSet0("__identity__", s);
	http->var[0] = s;
	return s;
}