Document rscrypt format upgrade path about password-hashes HOT 6 CLOSED

    fn upgrade_mcf_hash<'a>(&self, hash: &'a str) -> Result<PasswordHash<'a>> {
        let mut parts = hash.split('$');

        let buf = [
            parts.next(),
            parts.next(),
            parts.next(),
            parts.next(),
            parts.next(),
            parts.next(),
            parts.next(),
            parts.next(),
        ];

        let (log_n, r, p, salt, hash) = match buf {
            [Some(""), Some("rscrypt"), Some("0"), Some(p), Some(s), Some(h), Some(""), None] => {
                let pvec = Base64::decode_vec(p)?;
                if pvec.len() != 3 {
                    return Err(InvalidValue::Malformed.param_error());
                }
                (pvec[0], pvec[1] as u32, pvec[2] as u32, s, h)
            }
            [Some(""), Some("rscrypt"), Some("1"), Some(p), Some(s), Some(h), Some(""), None] => {
                let pvec = Base64::decode_vec(p)?;
                if pvec.len() != 9 {
                    return Err(InvalidValue::Malformed.param_error());
                }
                let log_n = pvec[0];
                let r = u32::from_le_bytes(pvec[1..5].try_into().unwrap());
                let p = u32::from_le_bytes(pvec[5..9].try_into().unwrap());
                (log_n, r, p, s, h)
            }
            _ => return Err(InvalidValue::Malformed.param_error()),
        };

        let params = Params::new(log_n, r, p).map_err(|_| InvalidValue::Malformed.param_error())?;

        let salt = Salt::new(b64_strip(salt))?;
        let hash = Output::b64_decode(b64_strip(hash))?;

        Ok(PasswordHash {
            algorithm: ALG_ID,
            version: None,
            params: params.try_into()?,
            salt: Some(salt),
            hash: Some(hash),
        })
    }