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    //! Credential provider that implements PASETO asymmetric tokens stored in Cargo's config.

    use anyhow::Context;
    use cargo_credential::{
        Action, CacheControl, Credential, CredentialResponse, Error, Operation, RegistryInfo, Secret,
    };
    use clap::Command;
    use pasetors::{
        keys::{AsymmetricKeyPair, AsymmetricPublicKey, AsymmetricSecretKey, Generate},
        paserk::FormatAsPaserk,
    };
    use time::{format_description::well_known::Rfc3339, OffsetDateTime};
    use url::Url;

    use crate::{
        core::SourceId,
        ops::RegistryCredentialConfig,
        util::{auth::registry_credential_config_raw, command_prelude::opt, config},
        Config,
    };

    /// The main body of an asymmetric token as describe in RFC 3231.
    #[derive(serde::Serialize)]
    struct Message<'a> {
        iat: &'a str,
        #[serde(skip_serializing_if = "Option::is_none")]
        sub: Option<&'a str>,
        #[serde(skip_serializing_if = "Option::is_none")]
        mutation: Option<&'a str>,
        #[serde(skip_serializing_if = "Option::is_none")]
        name: Option<&'a str>,
        #[serde(skip_serializing_if = "Option::is_none")]
        vers: Option<&'a str>,
        #[serde(skip_serializing_if = "Option::is_none")]
        cksum: Option<&'a str>,
        #[serde(skip_serializing_if = "Option::is_none")]
        challenge: Option<&'a str>,
        /// This field is not yet used. This field can be set to a value >1 to indicate a breaking change in the token format.
        #[serde(skip_serializing_if = "Option::is_none")]
        v: Option<u8>,
    }
    /// The footer of an asymmetric token as describe in RFC 3231.
    #[derive(serde::Serialize)]
    struct Footer<'a> {
        url: &'a str,
        kip: pasetors::paserk::Id,
    }

    pub(crate) struct PasetoCredential<'a> {
        config: &'a Config,
    }

    impl<'a> PasetoCredential<'a> {
        pub fn new(config: &'a Config) -> Self {
            Self { config }
        }
    }

    impl<'a> Credential for PasetoCredential<'a> {
        fn perform(
            &self,
            registry: &RegistryInfo<'_>,
            action: &Action<'_>,
            args: &[&str],
        ) -> Result<CredentialResponse, Error> {
            let index_url = Url::parse(registry.index_url).context("parsing index url")?;
            let sid = if let Some(name) = registry.name {
                SourceId::for_alt_registry(&index_url, name)
            } else {
                SourceId::for_registry(&index_url)
            }?;

            let reg_cfg = registry_credential_config_raw(self.config, &sid)?;

            let matches = Command::new("cargo:paseto")
                .no_binary_name(true)
                .arg(opt("key-subject", "Set the key subject for this registry").value_name("SUBJECT"))
                .try_get_matches_from(args)
                .map_err(Box::new)?;
            let key_subject = matches.get_one("key-subject").map(String::as_str);

            match action {
                Action::Get(operation) => {
                    let Some(reg_cfg) = reg_cfg else {
                        return Err(Error::NotFound);
                    };
                    let Some(secret_key) = reg_cfg.secret_key.as_ref() else {
                        return Err(Error::NotFound);
                    };

                    let secret_key_subject = reg_cfg.secret_key_subject;
                    let secret: Secret<AsymmetricSecretKey<pasetors::version3::V3>> = secret_key
                        .val
                        .as_ref()
                        .map(|key| key.as_str().try_into())
                        .transpose()
                        .context("failed to load private key")?;
                    let public: AsymmetricPublicKey<pasetors::version3::V3> = secret
                        .as_ref()
                        .map(|key| key.try_into())
                        .transpose()
                        .context("failed to load public key from private key")?
                        .expose();
                    let kip: pasetors::paserk::Id = (&public).into();

                    let iat = OffsetDateTime::now_utc();

                    let message = Message {
                        iat: &iat.format(&Rfc3339).unwrap(),
                        sub: secret_key_subject.as_deref(),
                        mutation: match operation {
                            Operation::Publish { .. } => Some("publish"),
                            Operation::Yank { .. } => Some("yank"),
                            Operation::Unyank { .. } => Some("unyank"),
                            Operation::Owners { .. } => Some("owners"),
                            _ => None,
                        },
                        name: match operation {
                            Operation::Publish { name, .. }
                            | Operation::Yank { name, .. }
                            | Operation::Unyank { name, .. }
                            | Operation::Owners { name, .. } => Some(name),
                            _ => None,
                        },
                        vers: match operation {
                            Operation::Publish { vers, .. }
                            | Operation::Yank { vers, .. }
                            | Operation::Unyank { vers, .. } => Some(vers),
                            _ => None,
                        },
                        cksum: match operation {
                            Operation::Publish { cksum, .. } => Some(cksum),
                            _ => None,
                        },
                        challenge: None, // todo: PASETO with challenges
                        v: None,
                    };
                    let footer = Footer {
                        url: &registry.index_url,
                        kip,
                    };

                    // Only read operations can be cached with asymmetric tokens.
                    let cache = match operation {
                        Operation::Read => CacheControl::Session,
                        _ => CacheControl::Never,
                    };

                    let token = secret
                        .map(|secret| {
                            pasetors::version3::PublicToken::sign(
                                &secret,
                                serde_json::to_string(&message)
                                    .expect("cannot serialize")
                                    .as_bytes(),
                                Some(
                                    serde_json::to_string(&footer)
                                        .expect("cannot serialize")
                                        .as_bytes(),
                                ),
                                None,
                            )
                        })
                        .transpose()
                        .context("failed to sign request")?;

                    Ok(CredentialResponse::Get {
                        token,
                        cache,
                        operation_independent: false,
                    })
                }
                Action::Login(options) => {
                    let old_key_subject = reg_cfg.and_then(|cfg| cfg.secret_key_subject);
                    let new_token;
                    let secret_key: Secret<String>;
                    if let Some(key) = &options.token {
                        secret_key = key.clone().map(str::to_string);
                    } else {
                        let kp = AsymmetricKeyPair::<pasetors::version3::V3>::generate().unwrap();
                        secret_key = Secret::default().map(|mut key| {
                            FormatAsPaserk::fmt(&kp.secret, &mut key).unwrap();
                            key
                        });
                    }

                    if let Some(p) = paserk_public_from_paserk_secret(secret_key.as_deref()) {
                        eprintln!("{}", &p);
                    } else {
                        return Err("not a validly formatted PASERK secret key".into());
                    }
                    new_token = RegistryCredentialConfig::AsymmetricKey((
                        secret_key,
                        match key_subject {
                            Some(key_subject) => Some(key_subject.to_string()),
                            None => old_key_subject,
                        },
                    ));
                    config::save_credentials(self.config, Some(new_token), &sid)?;
                    Ok(CredentialResponse::Login)
                }
                Action::Logout => {
                    if reg_cfg.and_then(|c| c.secret_key).is_some() {
                        config::save_credentials(self.config, None, &sid)?;
                        let reg_name = sid.display_registry_name();
                        let _ = self.config.shell().status(
                            "Logout",
                            format!("secret-key for `{reg_name}` has been removed from local storage"),
                        );
                        Ok(CredentialResponse::Logout)
                    } else {
                        Err(Error::NotFound)
                    }
                }
                _ => Err(Error::OperationNotSupported),
            }
        }
    }

    /// Checks that a secret key is valid, and returns the associated public key in Paserk format.
    pub(crate) fn paserk_public_from_paserk_secret(secret_key: Secret<&str>) -> Option<String> {
        let secret: Secret<AsymmetricSecretKey<pasetors::version3::V3>> =
            secret_key.map(|key| key.try_into()).transpose().ok()?;
        let public: AsymmetricPublicKey<pasetors::version3::V3> = secret
            .as_ref()
            .map(|key| key.try_into())
            .transpose()
            .ok()?
            .expose();
        let mut paserk_pub_key = String::new();
        FormatAsPaserk::fmt(&public, &mut paserk_pub_key).unwrap();
        Some(paserk_pub_key)
    }