code: public static ContextAwarePolicy createCalendarPolicy(Extender extender) {
          Util.notNull(extender, "Extender");
          return new ContextAwarePolicyAdapter(new CalendarBasedVerificationPolicy(),
                  new PolicyContext(extender.getExtendingService()));
      }
docs: Creates context aware policy using {@link CalendarBasedVerificationPolicy} for verification. Since
  extender is provided, then extending is allowed when verifying signature.
  
  @param extender
  Extender.
  @return Calendar based verification policy with suitable context.