cirrus_auth/

jwt.rs

//! OAuth 2.0 JWT Bearer flow for Salesforce server-to-server auth.
//!
//! The caller pre-authorizes a Connected App by uploading a public X.509
//! certificate; this auth implementation holds the corresponding RSA private
//! key and mints fresh access tokens on demand by signing a short-lived JWT
//! and exchanging it at the OAuth token endpoint.
//!
//! ## `instance_url`
//!
//! `instance_url` is required at builder time and verified against the
//! value returned in the token response.
//!
//! ## Caching
//!
//! Each successful token exchange caches the access token for a configurable
//! TTL (default 30 minutes). Salesforce does not return an explicit expiry
//! in the token response — the connected app's session policy controls
//! actual expiration — so the TTL is a conservative caller-controlled knob,
//! not a claim about the token's true lifetime. After the TTL elapses, the
//! next call mints a new token regardless of whether the previous one would
//! still have worked.

use crate::AuthSession;
use crate::error::{AuthError, AuthResult};
use crate::token_endpoint::{check_instance_url, exchange};
use async_trait::async_trait;
use camino::Utf8PathBuf;
use jsonwebtoken::{Algorithm, EncodingKey, Header};
use serde::Serialize;
use std::borrow::Cow;
use std::time::{Duration, Instant, SystemTime, UNIX_EPOCH};
use tokio::sync::RwLock;

/// Salesforce production login URL — the default JWT audience and token
/// exchange host.
pub const PRODUCTION_LOGIN_URL: &str = "https://login.salesforce.com";

/// Salesforce sandbox login URL.
pub const SANDBOX_LOGIN_URL: &str = "https://test.salesforce.com";

/// Default cache TTL for an access token after it's issued.
const DEFAULT_TOKEN_TTL: Duration = Duration::from_secs(30 * 60);

/// JWT validity window. Salesforce rejects assertions whose `exp` is
/// more than 3 minutes ahead of *its* clock. Setting `exp = now + 180`
/// leaves zero slack: any clock skew where the local host runs even
/// slightly ahead of Salesforce will push `exp` over the ceiling and
/// produce `invalid_grant`. The 10-second buffer below keeps the
/// assertion short-lived while tolerating the kind of skew typical of
/// NTP-synced machines.
const JWT_VALIDITY_SECS: i64 = 170;

#[derive(Serialize)]
struct JwtClaims {
    iss: String,
    sub: String,
    aud: String,
    exp: i64,
}

// `iss` is the Connected App consumer key (a credential identifier) and
// `sub` is the Salesforce username (PII). Redact both so a stray
// `{:?}` in error-handling code never leaks them.
impl std::fmt::Debug for JwtClaims {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("JwtClaims")
            .field("iss", &"[redacted]")
            .field("sub", &"[redacted]")
            .field("aud", &self.aud)
            .field("exp", &self.exp)
            .finish()
    }
}

#[derive(Clone)]
struct CachedToken {
    access_token: String,
    expires_at: Instant,
}

impl std::fmt::Debug for CachedToken {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("CachedToken")
            .field("access_token", &"[redacted]")
            .field("expires_at", &self.expires_at)
            .finish()
    }
}

/// JWT Bearer flow auth session.
///
/// Construct via [`JwtAuth::builder`].
pub struct JwtAuth {
    consumer_key: String,
    username: String,
    encoding_key: EncodingKey,
    login_url: String,
    instance_url: String,
    token_ttl: Duration,
    http: reqwest::Client,
    cached: RwLock<Option<CachedToken>>,
}

impl std::fmt::Debug for JwtAuth {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        // Deliberately omit consumer_key, username, and the encoding key —
        // all carry secrets or PII.
        f.debug_struct("JwtAuth")
            .field("login_url", &self.login_url)
            .field("instance_url", &self.instance_url)
            .field("token_ttl", &self.token_ttl)
            .finish_non_exhaustive()
    }
}

impl JwtAuth {
    /// Begins constructing a [`JwtAuth`].
    ///
    /// JWT bearer flow (RFC 7523): the SDK signs a JWT assertion with
    /// your connected app's private key and exchanges it for an access
    /// token at the configured login URL. Cached access tokens are
    /// refreshed transparently on 401.
    ///
    /// # Example
    ///
    /// ```no_run
    /// use cirrus_auth::JwtAuth;
    /// use std::sync::Arc;
    ///
    /// # fn example() -> Result<(), cirrus_auth::AuthError> {
    /// let auth = JwtAuth::builder()
    ///     .consumer_key("3MVG9...")
    ///     .username("integration-user@example.com")
    ///     .login_url("https://login.salesforce.com")
    ///     .instance_url("https://my-org.my.salesforce.com")
    ///     .private_key_pem_file("./private.pem")?
    ///     .build()?;
    /// // Wrap as Arc<dyn AuthSession> and hand to a Cirrus client.
    /// let _shared = Arc::new(auth);
    /// # Ok(())
    /// # }
    /// ```
    pub fn builder() -> JwtAuthBuilder {
        JwtAuthBuilder::default()
    }

    async fn mint_token(&self) -> AuthResult<CachedToken> {
        tracing::info!(
            target: "cirrus::auth",
            flow = "jwt-bearer",
            login_url = %self.login_url,
            "minting fresh access token",
        );
        let now_secs = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .map(|d| d.as_secs() as i64)
            .map_err(|e| AuthError::Other(format!("system clock before UNIX epoch: {e}")))?;

        let claims = JwtClaims {
            iss: self.consumer_key.clone(),
            sub: self.username.clone(),
            aud: self.login_url.clone(),
            exp: now_secs + JWT_VALIDITY_SECS,
        };

        let header = Header::new(Algorithm::RS256);
        let assertion = jsonwebtoken::encode(&header, &claims, &self.encoding_key)
            .map_err(|e| AuthError::Other(format!("JWT signing failed: {e}")))?;

        let body = [
            ("grant_type", "urn:ietf:params:oauth:grant-type:jwt-bearer"),
            ("assertion", assertion.as_str()),
        ];

        let token = exchange(&self.http, &self.login_url, &body).await?;
        check_instance_url(&self.instance_url, &token)?;

        Ok(CachedToken {
            access_token: token.access_token,
            expires_at: Instant::now() + self.token_ttl,
        })
    }
}

#[async_trait]
impl AuthSession for JwtAuth {
    async fn access_token(&self) -> AuthResult<Cow<'_, str>> {
        // Fast path — read lock, return clone of cached token if still valid.
        {
            let guard = self.cached.read().await;
            if let Some(cached) = guard.as_ref()
                && cached.expires_at > Instant::now()
            {
                return Ok(Cow::Owned(cached.access_token.clone()));
            }
        }

        // Slow path — write lock, double-check, mint.
        let mut guard = self.cached.write().await;
        if let Some(cached) = guard.as_ref()
            && cached.expires_at > Instant::now()
        {
            return Ok(Cow::Owned(cached.access_token.clone()));
        }
        let new_token = self.mint_token().await?;
        let token_str = new_token.access_token.clone();
        *guard = Some(new_token);
        Ok(Cow::Owned(token_str))
    }

    fn instance_url(&self) -> &str {
        &self.instance_url
    }

    async fn invalidate(&self, stale_token: &str) {
        // Compare-and-swap: only clear the cached token if it still
        // matches what the failing request used. Avoids racing with a
        // concurrent task that already refreshed.
        let mut guard = self.cached.write().await;
        if let Some(cached) = guard.as_ref()
            && cached.access_token == stale_token
        {
            tracing::debug!(
                target: "cirrus::auth",
                flow = "jwt-bearer",
                "invalidating cached token (CAS matched)",
            );
            *guard = None;
        } else {
            tracing::trace!(
                target: "cirrus::auth",
                flow = "jwt-bearer",
                "invalidate called but cached token differs (concurrent refresh?); no-op",
            );
        }
    }
}

/// Builder for [`JwtAuth`].
#[derive(Default)]
pub struct JwtAuthBuilder {
    consumer_key: Option<String>,
    username: Option<String>,
    encoding_key: Option<EncodingKey>,
    login_url: Option<String>,
    instance_url: Option<String>,
    token_ttl: Option<Duration>,
    http_client: Option<reqwest::Client>,
}

impl std::fmt::Debug for JwtAuthBuilder {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        // Show which fields have been set without leaking secret-bearing values.
        f.debug_struct("JwtAuthBuilder")
            .field("consumer_key", &self.consumer_key.is_some())
            .field("username", &self.username.is_some())
            .field("private_key", &self.encoding_key.is_some())
            .field("login_url", &self.login_url)
            .field("instance_url", &self.instance_url)
            .field("token_ttl", &self.token_ttl)
            .finish_non_exhaustive()
    }
}

impl JwtAuthBuilder {
    /// Connected App's Consumer Key (a.k.a. Client ID) — used as the JWT
    /// `iss` claim.
    pub fn consumer_key(mut self, key: impl Into<String>) -> Self {
        self.consumer_key = Some(key.into());
        self
    }

    /// Salesforce username to authenticate as — used as the JWT `sub` claim.
    pub fn username(mut self, username: impl Into<String>) -> Self {
        self.username = Some(username.into());
        self
    }

    /// Loads the RSA private key from a PEM file at the given path.
    pub fn private_key_pem_file(mut self, path: impl Into<Utf8PathBuf>) -> AuthResult<Self> {
        let path = path.into();
        let bytes = fs_err::read(path.as_std_path())
            .map_err(|e| AuthError::Other(format!("failed to read private key: {e}")))?;
        self.encoding_key = Some(
            EncodingKey::from_rsa_pem(&bytes)
                .map_err(|e| AuthError::Other(format!("invalid RSA PEM key: {e}")))?,
        );
        Ok(self)
    }

    /// Loads the RSA private key directly from PEM-encoded bytes. Useful
    /// when the key is held in memory (e.g. fetched from a secret manager).
    pub fn private_key_pem_bytes(mut self, bytes: &[u8]) -> AuthResult<Self> {
        self.encoding_key = Some(
            EncodingKey::from_rsa_pem(bytes)
                .map_err(|e| AuthError::Other(format!("invalid RSA PEM key: {e}")))?,
        );
        Ok(self)
    }

    /// Login URL — the host that receives the JWT, also used as the JWT
    /// `aud` claim. Defaults to [`PRODUCTION_LOGIN_URL`]. Use
    /// [`SANDBOX_LOGIN_URL`] for sandboxes.
    ///
    /// Per Salesforce docs ("OAuth 2.0 JWT Bearer Flow ... aud"), valid
    /// audience values are `https://login.salesforce.com`,
    /// `https://test.salesforce.com`, or an Experience Cloud site URL —
    /// **not** the org's My Domain. The `instance_url` is what points at
    /// the org; this URL identifies the authorization server.
    pub fn login_url(mut self, url: impl Into<String>) -> Self {
        self.login_url = Some(url.into());
        self
    }

    /// REST instance URL — the org's My Domain (e.g.
    /// `https://my-org.my.salesforce.com`). Required. Must match the
    /// `instance_url` that Salesforce returns from the token exchange.
    pub fn instance_url(mut self, url: impl Into<String>) -> Self {
        self.instance_url = Some(url.into());
        self
    }

    /// How long to cache an access token before re-minting. Defaults to 30
    /// minutes. Set lower to refresh more aggressively, or higher if your
    /// connected app's session policy allows.
    pub fn token_ttl(mut self, ttl: Duration) -> Self {
        self.token_ttl = Some(ttl);
        self
    }

    /// Supplies a pre-configured `reqwest::Client` for the token-exchange
    /// requests. Useful for sharing a connection pool across multiple SDK
    /// clients.
    pub fn http_client(mut self, client: reqwest::Client) -> Self {
        self.http_client = Some(client);
        self
    }

    /// Finalizes the builder.
    pub fn build(self) -> AuthResult<JwtAuth> {
        let consumer_key = self
            .consumer_key
            .ok_or(AuthError::MissingField("consumer_key"))?;
        let username = self.username.ok_or(AuthError::MissingField("username"))?;
        let encoding_key = self
            .encoding_key
            .ok_or(AuthError::MissingField("private_key"))?;
        let mut instance_url = self
            .instance_url
            .ok_or(AuthError::MissingField("instance_url"))?;
        if instance_url.ends_with('/') {
            instance_url.pop();
        }
        let mut login_url = self
            .login_url
            .unwrap_or_else(|| PRODUCTION_LOGIN_URL.to_string());
        if login_url.ends_with('/') {
            login_url.pop();
        }
        let token_ttl = self.token_ttl.unwrap_or(DEFAULT_TOKEN_TTL);
        let http = self.http_client.unwrap_or_default();

        Ok(JwtAuth {
            consumer_key,
            username,
            encoding_key,
            login_url,
            instance_url,
            token_ttl,
            http,
            cached: RwLock::new(None),
        })
    }
}

#[cfg(test)]
#[allow(clippy::unwrap_used, clippy::expect_used, clippy::panic)]
mod tests {
    use super::*;
    use std::sync::Arc;
    use std::sync::atomic::{AtomicUsize, Ordering};
    use wiremock::matchers::{body_string_contains, method, path};
    use wiremock::{Mock, MockServer, Request, Respond, ResponseTemplate};

    /// Throwaway test-only RSA private key. No security value.
    /// See `tests/fixtures/test_rsa_key.pem`.
    const TEST_PEM: &[u8] = include_bytes!("../tests/fixtures/test_rsa_key.pem");

    fn builder_with_required_fields() -> JwtAuthBuilder {
        JwtAuth::builder()
            .consumer_key("consumer-key-123")
            .username("integration@example.com")
            .private_key_pem_bytes(TEST_PEM)
            .unwrap()
            .instance_url("https://my-org.my.salesforce.com")
    }

    #[test]
    fn builder_requires_consumer_key() {
        let err = JwtAuth::builder()
            .username("u")
            .private_key_pem_bytes(TEST_PEM)
            .unwrap()
            .instance_url("https://x")
            .build()
            .unwrap_err();
        assert!(matches!(err, AuthError::MissingField("consumer_key")));
    }

    #[test]
    fn builder_requires_username() {
        let err = JwtAuth::builder()
            .consumer_key("k")
            .private_key_pem_bytes(TEST_PEM)
            .unwrap()
            .instance_url("https://x")
            .build()
            .unwrap_err();
        assert!(matches!(err, AuthError::MissingField("username")));
    }

    #[test]
    fn builder_requires_private_key() {
        let err = JwtAuth::builder()
            .consumer_key("k")
            .username("u")
            .instance_url("https://x")
            .build()
            .unwrap_err();
        assert!(matches!(err, AuthError::MissingField("private_key")));
    }

    #[test]
    fn builder_requires_instance_url() {
        let err = JwtAuth::builder()
            .consumer_key("k")
            .username("u")
            .private_key_pem_bytes(TEST_PEM)
            .unwrap()
            .build()
            .unwrap_err();
        assert!(matches!(err, AuthError::MissingField("instance_url")));
    }

    #[test]
    fn invalid_pem_is_surfaced_as_auth_error() {
        let err = JwtAuth::builder()
            .private_key_pem_bytes(b"not a pem")
            .unwrap_err();
        assert!(matches!(err, AuthError::Other(_)));
    }

    #[test]
    fn builder_strips_trailing_slashes_and_defaults_login_url() {
        let auth = builder_with_required_fields()
            .instance_url("https://my-org.my.salesforce.com/")
            .build()
            .unwrap();
        assert_eq!(auth.instance_url(), "https://my-org.my.salesforce.com");
        assert_eq!(auth.login_url, PRODUCTION_LOGIN_URL);
    }

    #[tokio::test]
    async fn mint_token_succeeds_and_caches() {
        let server = MockServer::start().await;
        let hits = Arc::new(AtomicUsize::new(0));
        let body = serde_json::json!({
            "access_token": "00DXX!ACCESS",
            "instance_url": "https://my-org.my.salesforce.com",
            "token_type": "Bearer",
            "scope": "api",
            "id": "https://login.salesforce.com/id/00DXX/005XX",
        });

        Mock::given(method("POST"))
            .and(path("/services/oauth2/token"))
            .and(body_string_contains("grant_type=urn"))
            .and(body_string_contains("assertion="))
            .respond_with(CountingResponder {
                hits: hits.clone(),
                response: ResponseTemplate::new(200).set_body_json(body),
            })
            .mount(&server)
            .await;

        let auth = builder_with_required_fields()
            .login_url(server.uri())
            .build()
            .unwrap();

        let t1 = auth.access_token().await.unwrap();
        assert_eq!(&*t1, "00DXX!ACCESS");
        let t2 = auth.access_token().await.unwrap();
        assert_eq!(&*t2, "00DXX!ACCESS");

        // Second call must reuse the cached token, not call the endpoint again.
        assert_eq!(hits.load(Ordering::SeqCst), 1);
    }

    #[tokio::test]
    async fn expired_cache_remints_token() {
        let server = MockServer::start().await;
        let hits = Arc::new(AtomicUsize::new(0));

        Mock::given(method("POST"))
            .and(path("/services/oauth2/token"))
            .respond_with(CountingResponder {
                hits: hits.clone(),
                response: ResponseTemplate::new(200).set_body_json(serde_json::json!({
                    "access_token": "tok",
                    "instance_url": "https://my-org.my.salesforce.com"
                })),
            })
            .mount(&server)
            .await;

        let auth = builder_with_required_fields()
            .login_url(server.uri())
            .token_ttl(Duration::ZERO) // every call re-mints
            .build()
            .unwrap();

        let _ = auth.access_token().await.unwrap();
        let _ = auth.access_token().await.unwrap();
        let _ = auth.access_token().await.unwrap();

        assert_eq!(hits.load(Ordering::SeqCst), 3);
    }

    #[tokio::test]
    async fn oauth_error_response_is_surfaced() {
        let server = MockServer::start().await;
        Mock::given(method("POST"))
            .and(path("/services/oauth2/token"))
            .respond_with(ResponseTemplate::new(400).set_body_json(serde_json::json!({
                "error": "invalid_grant",
                "error_description": "user hasn't approved this consumer"
            })))
            .mount(&server)
            .await;

        let auth = builder_with_required_fields()
            .login_url(server.uri())
            .build()
            .unwrap();

        let err = auth.access_token().await.unwrap_err();
        match err {
            AuthError::OAuth {
                error,
                error_description,
            } => {
                assert_eq!(error, "invalid_grant");
                assert!(error_description.is_some());
            }
            other => panic!("expected OAuth error, got {other:?}"),
        }
    }

    #[tokio::test]
    async fn instance_url_mismatch_is_an_auth_error() {
        let server = MockServer::start().await;
        Mock::given(method("POST"))
            .and(path("/services/oauth2/token"))
            .respond_with(ResponseTemplate::new(200).set_body_json(serde_json::json!({
                "access_token": "tok",
                "instance_url": "https://different-org.my.salesforce.com"
            })))
            .mount(&server)
            .await;

        let auth = builder_with_required_fields()
            .login_url(server.uri())
            .build()
            .unwrap();

        let err = auth.access_token().await.unwrap_err();
        assert!(matches!(err, AuthError::Other(_)));
    }

    /// `invalidate(stale_token)` is a compare-and-swap: it should
    /// only clear the cached token when the cached value matches
    /// `stale_token`. This is the contract for all three flows
    /// (Jwt, Refresh, ClientCredentials); we test it here as the
    /// canonical example since the impls are identical.
    #[tokio::test]
    async fn invalidate_clears_cache_only_when_stale_token_matches() {
        let server = MockServer::start().await;
        let hits = Arc::new(AtomicUsize::new(0));
        let body = serde_json::json!({
            "access_token": "T1",
            "instance_url": "https://my-org.my.salesforce.com",
            "token_type": "Bearer",
        });

        Mock::given(method("POST"))
            .and(path("/services/oauth2/token"))
            .respond_with(CountingResponder {
                hits: hits.clone(),
                response: ResponseTemplate::new(200).set_body_json(body),
            })
            .mount(&server)
            .await;

        let auth = builder_with_required_fields()
            .login_url(server.uri())
            .build()
            .unwrap();

        // First call mints T1; cache populated.
        let t = auth.access_token().await.unwrap();
        assert_eq!(&*t, "T1");
        assert_eq!(hits.load(Ordering::SeqCst), 1);
        drop(t);

        // Invalidate with a *non-matching* stale_token — should be a
        // no-op, cache stays populated.
        auth.invalidate("not-the-cached-token").await;
        let t = auth.access_token().await.unwrap();
        assert_eq!(&*t, "T1");
        // No re-mint — the cache wasn't cleared.
        assert_eq!(hits.load(Ordering::SeqCst), 1);
        drop(t);

        // Invalidate with the *matching* stale_token — clears cache.
        auth.invalidate("T1").await;
        // Next access call must re-mint.
        let t = auth.access_token().await.unwrap();
        assert_eq!(&*t, "T1"); // mock still returns T1
        assert_eq!(hits.load(Ordering::SeqCst), 2);
    }

    /// Wraps a [`ResponseTemplate`] and counts invocations. Wiremock's
    /// `expect()` would also work, but counting lets us assert post-hoc.
    struct CountingResponder {
        hits: Arc<AtomicUsize>,
        response: ResponseTemplate,
    }

    impl Respond for CountingResponder {
        fn respond(&self, _: &Request) -> ResponseTemplate {
            self.hits.fetch_add(1, Ordering::SeqCst);
            self.response.clone()
        }
    }
}