code: public void initialize(Subject subject, CallbackHandler callbackHandler,
        Map<String, ?> sharedState, Map<String, ?> options) {
      this.subject = subject;
      this.callbackHandler = callbackHandler;
      this.principals.clear();
      this.publicCredentials.clear();
      this.privateCredentials.clear();
      this.initialize(sharedState, options);
    }
docs: /* (non-Javadoc)
  @see javax.security.auth.spi.LoginModule#initialize(javax.security.auth.Subject, javax.security.auth.callback.CallbackHandler, java.util.Map, java.util.Map)