huskarl 0.9.1

//! Refresh token grant (RFC 6749 §6).
//!
//! Used to obtain a new access token using a previously issued refresh token,
//! without requiring the user to re-authenticate. Most often created from an
//! existing grant via `to_refresh_grant`, which inherits its client
//! authentication, `DPoP`, and HTTP client settings.
//!
//! See the [refresh token how-to guide](crate::_docs::guide::refresh) for
//! step-by-step setup.

use std::sync::Arc;

use bon::Builder;
use serde::Serialize;

use crate::{
    core::{
        EndpointUrl,
        client_auth::ClientAuthentication,
        dpop::{AuthorizationServerDPoP, NoDPoP},
        http::HttpClient,
        secrets::SecretString,
    },
    grant::core::{OAuth2ExchangeGrant, join_space},
    token::RefreshToken,
};

/// An `OAuth2` refresh grant (RFC 6749 §6).
///
/// Exchanges a refresh token from a previous token-endpoint response for a new
/// access token. See the [module documentation][crate::grant::refresh] for a
/// usage guide.
#[huskarl_macros::from_metadata(metadata = crate::core::server_metadata::AuthorizationServerMetadata)]
#[derive(Clone, Builder)]
#[builder(on(String, into))]
pub struct RefreshGrant {
    /// The client ID. Omitted for a client that presents no identification
    /// (e.g. refreshing a token obtained by an anonymous grant).
    client_id: Option<String>,

    /// The HTTP client used for token requests.
    #[builder(with = |client: impl HttpClient + 'static| Arc::new(client) as Arc<dyn HttpClient>)]
    http_client: Arc<dyn HttpClient>,

    /// The client authentication method. Omitted for a public client that does
    /// not authenticate to the token endpoint (RFC 6749 §6).
    #[builder(with = |auth: impl ClientAuthentication + 'static| Arc::new(auth) as Arc<dyn ClientAuthentication>)]
    client_auth: Option<Arc<dyn ClientAuthentication>>,

    /// The `DPoP` signer. Defaults to [`NoDPoP`] (no token sender-constraining).
    #[builder(
        with = |dpop: impl AuthorizationServerDPoP + 'static| Arc::new(dpop) as Arc<dyn AuthorizationServerDPoP>,
        default = Arc::new(NoDPoP),
    )]
    dpop: Arc<dyn AuthorizationServerDPoP>,

    /// The issuer for tokens created by the authorization server.
    #[from_metadata(path = "issuer")]
    issuer: Option<String>,

    /// The URL of the token endpoint.
    #[from_metadata(path = "token_endpoint")]
    token_endpoint: EndpointUrl,

    /// The mTLS alias for the token endpoint (RFC 8705 §5).
    #[from_metadata(path = "mtls_endpoint_aliases?.token_endpoint?")]
    mtls_token_endpoint: Option<EndpointUrl>,

    /// The endpoint used for token requests: the mTLS alias when the HTTP
    /// client uses mTLS, the primary token endpoint otherwise.
    #[builder(skip = crate::grant::core::resolve_mtls_alias(http_client.as_ref(), &token_endpoint, mtls_token_endpoint.as_ref()))]
    effective_token_endpoint: EndpointUrl,

    /// Supported endpoint auth methods; used to auto-select basic or
    /// form auth for client secrets.
    #[from_metadata(path = "token_endpoint_auth_methods_supported")]
    token_endpoint_auth_methods_supported: Option<Vec<String>>,
}

impl core::fmt::Debug for RefreshGrant {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        f.debug_struct("RefreshGrant")
            .field("client_id", &self.client_id)
            .field("issuer", &self.issuer)
            .field("token_endpoint", &self.token_endpoint)
            .field("mtls_token_endpoint", &self.mtls_token_endpoint)
            .finish_non_exhaustive()
    }
}

impl OAuth2ExchangeGrant for RefreshGrant {
    type Parameters = RefreshGrantParameters;
    type Form<'a> = RefreshGrantForm;

    fn client_id(&self) -> Option<&str> {
        self.client_id.as_deref()
    }

    fn issuer(&self) -> Option<&str> {
        self.issuer.as_deref()
    }

    fn client_auth(&self) -> Option<&dyn ClientAuthentication> {
        self.client_auth.as_deref()
    }

    fn token_endpoint(&self) -> &EndpointUrl {
        &self.token_endpoint
    }

    fn effective_token_endpoint(&self) -> &EndpointUrl {
        &self.effective_token_endpoint
    }

    fn dpop(&self) -> &dyn AuthorizationServerDPoP {
        self.dpop.as_ref()
    }

    fn http_client(&self) -> &dyn HttpClient {
        self.http_client.as_ref()
    }

    fn allowed_auth_methods(&self) -> Option<&[String]> {
        self.token_endpoint_auth_methods_supported.as_deref()
    }

    fn to_refresh_grant(&self) -> RefreshGrant {
        self.clone()
    }

    fn bound_dpop_jkt(params: &Self::Parameters) -> Option<&str> {
        params.refresh_token.dpop_jkt()
    }

    fn build_form(&self, params: Self::Parameters) -> Self::Form<'_> {
        RefreshGrantForm {
            grant_type: "refresh_token",
            refresh_token: params.refresh_token.token().clone(),
            scope: join_space(params.scope.as_deref()),
            resource: params.resource,
            authorization_details: params.authorization_details,
        }
    }
}

/// Parameters when requesting a token using the refresh grant.
#[derive(Debug, Clone, Builder)]
pub struct RefreshGrantParameters {
    /// The refresh token to use in the refresh token request.
    refresh_token: RefreshToken,
    /// Scopes for downscoping (must be previously granted scopes).
    scope: Option<Vec<String>>,
    /// The target resource(s) for the access token.
    resource: Option<Vec<String>>,
    /// RFC 9396 `authorization_details` requested for the issued access token.
    authorization_details: Option<Vec<crate::core::AuthorizationDetail>>,
}

impl RefreshGrantParameters {
    /// Implements a simple set of parameters to the grant including just the refresh token.
    ///
    /// This is enough for most use cases; the builder exists as an extensible
    /// API where arbitrary extra fields may be added in future.
    #[must_use]
    pub fn refresh_token(token: RefreshToken) -> Self {
        Self::builder().refresh_token(token).build()
    }
}

/// Refresh grant body.
#[derive(Debug, Serialize, Builder)]
pub struct RefreshGrantForm {
    grant_type: &'static str,
    refresh_token: SecretString,
    scope: Option<String>,
    resource: Option<Vec<String>>,
    /// RFC 9396 `authorization_details` requested for the issued access token.
    authorization_details: Option<Vec<crate::core::AuthorizationDetail>>,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn refresh_form_serializes_token_as_plain_string() {
        let form = RefreshGrantForm::builder()
            .grant_type("refresh_token")
            .refresh_token(SecretString::new("my-refresh-token"))
            .build();
        let encoded = crate::core::oauth_form::to_string(&form).unwrap();
        assert_eq!(
            encoded,
            "grant_type=refresh_token&refresh_token=my-refresh-token"
        );
    }

    #[test]
    fn refresh_form_resource_serializes_as_repeated_keys() {
        let form = RefreshGrantForm::builder()
            .grant_type("refresh_token")
            .refresh_token(SecretString::new("tok"))
            .resource(vec![
                "https://api.example.com".into(),
                "https://other.example.com".into(),
            ])
            .build();
        let encoded = crate::core::oauth_form::to_string(&form).unwrap();
        assert!(
            encoded.contains("resource=https%3A%2F%2Fapi.example.com"),
            "first resource not found in: {encoded}"
        );
        assert!(
            encoded.contains("resource=https%3A%2F%2Fother.example.com"),
            "second resource not found in: {encoded}"
        );
        assert!(
            !encoded.contains(','),
            "resource values should not be comma-joined: {encoded}"
        );
    }
}