public String authenticate() {
		User user = DataProvider.getUser(username, password);
		if (user == null) {
			if(session.containsKey(USER_OBJ))
				session.remove(USER_OBJ);
			addActionError(getText("error.login"));
			return ERROR;
		}
		session.put(USER_OBJ, user);
		return SUCCESS;
	}