* @throws UnsupportedOperationException always thrown as this method is not supported
     */
    @Override
    protected void checkCredential(final TypicalLoginAssist<String, FessUserBean, FessUser>.CredentialChecker checker) {
        throw new UnsupportedOperationException("checkCredential is not supported.");
    }

    /**
     * Finds a login user by username.
     *
     * @param username the username to search for