public string setForumPasswordLifespan(string forumName, int lifespan, string requestingUser)
        {
            List <string> input = new List <string>()
            {
                forumName
            };

            if (Constants.isValidInput(input) && lifespan >= 0)
            {
                lock (o)
                {
                    if (_um.getUserPermissionsForForum(forumName, requestingUser) != permission.SUPER_ADMIN && _um.getUserPermissionsForForum(forumName, requestingUser) != permission.ADMIN)
                    {
                        return("Unauthorized user");
                    }
                    if (!_fm.setForumPasswordLifespan(forumName, lifespan))
                    {
                        return(Constants.forumDoesntExist(forumName));
                    }
                    // notify users with expired passwords
                    _um.notifyUsersThatNeedToUpdatePassword(forumName, lifespan);
                    return(Constants.SUCCESS);
                }
            }
            return(Constants.INVALID_INPUT);
        }