code: public boolean logout() {
      subject.getPrincipals().removeAll(principals);
      subject.getPrivateCredentials().removeAll(privateCredentials);
      subject.getPublicCredentials().removeAll(publicCredentials);
      principals.clear();
      privateCredentials.clear();
      publicCredentials.clear();
      return true;
    }
docs: /* (non-Javadoc)
  @see javax.security.auth.spi.LoginModule#logout()