pub fn check_user<U, P>(&self, user_name: U, password: P) -> bool
    where
        U: AsRef<str>,
        P: AsRef<str>,
    {
        match self.passwd.get(user_name.as_ref()) {
            Some(pwd) => pwd == password.as_ref(),
            None => false,
        }
    }
Check if `user_name` exists and validate `password`
crates/shadowsocks-service/src/local/socks/config.rs