feat(oidc): support multiple signing keys (#26)

* chore: update copyright license

* refactor: accept multiple signing keys

* chore: fix examples

Author: alukach

crates/oidc-provider/src/jwks.rs

@@ -4,31 +4,31 @@ use base64::Engine;
 use rsa::traits::PublicKeyParts;
 use rsa::RsaPublicKey;
 
-/// Generate a JWKS JSON response containing the proxy's RSA public key.
+/// Generate a JWKS JSON response containing one or more RSA public keys.
 ///
 /// This is served at the JWKS URI referenced by the OIDC discovery document,
 /// allowing relying parties (cloud providers) to verify JWTs signed by the proxy.
-pub fn jwks_json(public_key: &RsaPublicKey, kid: &str) -> String {
+/// Multiple keys support key rotation.
+pub fn jwks_json(keys: &[(&RsaPublicKey, &str)]) -> String {
     let b64 = &base64::engine::general_purpose::URL_SAFE_NO_PAD;
 
-    let n = public_key.n();
-    let e = public_key.e();
-
-    let n_b64 = b64.encode(n.to_bytes_be());
-    let e_b64 = b64.encode(e.to_bytes_be());
-
-    let jwks = serde_json::json!({
-        "keys": [{
-            "kty": "RSA",
-            "alg": "RS256",
-            "use": "sig",
-            "kid": kid,
-            "n": n_b64,
-            "e": e_b64,
-        }]
-    });
-
-    jwks.to_string()
+    let jwk_entries: Vec<serde_json::Value> = keys
+        .iter()
+        .map(|(public_key, kid)| {
+            let n_b64 = b64.encode(public_key.n().to_bytes_be());
+            let e_b64 = b64.encode(public_key.e().to_bytes_be());
+            serde_json::json!({
+                "kty": "RSA",
+                "alg": "RS256",
+                "use": "sig",
+                "kid": kid,
+                "n": n_b64,
+                "e": e_b64,
+            })
+        })
+        .collect();
+
+    serde_json::json!({ "keys": jwk_entries }).to_string()
 }
 
 #[cfg(test)]
@@ -42,7 +42,7 @@ mod tests {
         let private_key = RsaPrivateKey::new(&mut rng, 2048).unwrap();
         let public_key: &RsaPublicKey = private_key.as_ref();
 
-        let json_str = jwks_json(public_key, "my-kid");
+        let json_str = jwks_json(&[(public_key, "my-kid")]);
         let parsed: serde_json::Value = serde_json::from_str(&json_str).unwrap();
 
         let keys = parsed["keys"].as_array().unwrap();
@@ -57,6 +57,23 @@ mod tests {
         assert!(key["e"].as_str().unwrap().len() > 0);
     }
 
+    #[test]
+    fn jwks_contains_multiple_keys() {
+        let mut rng = rand::rngs::OsRng;
+        let key1 = RsaPrivateKey::new(&mut rng, 2048).unwrap();
+        let pub1: &RsaPublicKey = key1.as_ref();
+        let key2 = RsaPrivateKey::new(&mut rng, 2048).unwrap();
+        let pub2: &RsaPublicKey = key2.as_ref();
+
+        let json_str = jwks_json(&[(pub1, "kid-1"), (pub2, "kid-2")]);
+        let parsed: serde_json::Value = serde_json::from_str(&json_str).unwrap();
+
+        let keys = parsed["keys"].as_array().unwrap();
+        assert_eq!(keys.len(), 2);
+        assert_eq!(keys[0]["kid"], "kid-1");
+        assert_eq!(keys[1]["kid"], "kid-2");
+    }
+
     #[test]
     fn jwks_roundtrips_through_rsa() {
         use rsa::BigUint;
@@ -65,7 +82,7 @@ mod tests {
         let private_key = RsaPrivateKey::new(&mut rng, 2048).unwrap();
         let public_key: &RsaPublicKey = private_key.as_ref();
 
-        let json_str = jwks_json(public_key, "k1");
+        let json_str = jwks_json(&[(public_key, "k1")]);
         let parsed: serde_json::Value = serde_json::from_str(&json_str).unwrap();
 
         let key = &parsed["keys"][0];

crates/oidc-provider/src/lib.rs

@@ -283,7 +283,7 @@ mod tests {
         let token = signer.sign("sub", "iss", "aud", &[]).unwrap();
 
         // Generate JWKS from the same signer
-        let jwks_str = jwks::jwks_json(signer.public_key(), signer.kid());
+        let jwks_str = jwks::jwks_json(&[(signer.public_key(), signer.kid())]);
         let jwks: serde_json::Value = serde_json::from_str(&jwks_str).unwrap();
 
         // Extract public key from JWKS

crates/oidc-provider/src/route_handler.rs

@@ -27,15 +27,20 @@ impl RouteHandler for OidcConfigHandler {
 
 /// Handler that serves the JWKS (JSON Web Key Set) document.
 struct OidcJwksHandler {
-    signer: JwtSigner,
+    signers: Vec<JwtSigner>,
 }
 
 impl RouteHandler for OidcJwksHandler {
     fn handle<'a>(&'a self, req: &'a RequestInfo<'a>) -> RouteHandlerFuture<'a> {
         if req.method.as_str() != "GET" {
             return Box::pin(async { None });
         }
-        let json = jwks_json(self.signer.public_key(), self.signer.kid());
+        let keys: Vec<_> = self
+            .signers
+            .iter()
+            .map(|s| (s.public_key(), s.kid()))
+            .collect();
+        let json = jwks_json(&keys);
         Box::pin(async move { Some(ProxyResult::json(200, json)) })
     }
 }
@@ -44,17 +49,20 @@ impl RouteHandler for OidcJwksHandler {
 pub trait OidcRouterExt {
     /// Register `/.well-known/openid-configuration` and `/.well-known/jwks.json`
     /// routes backed by the given issuer and signer.
-    fn with_oidc_discovery(self, issuer: String, signer: JwtSigner) -> Self;
+    ///
+    /// `additional_signers` contains previous keys that should still appear in
+    /// the JWKS for key rotation (they are not used for signing new tokens).
+    fn with_oidc_discovery(self, issuer: String, signers: Vec<JwtSigner>) -> Self;
 }
 
 impl OidcRouterExt for Router {
-    fn with_oidc_discovery(self, issuer: String, signer: JwtSigner) -> Self {
+    fn with_oidc_discovery(self, issuer: String, signers: Vec<JwtSigner>) -> Self {
         let jwks_uri = format!("{}/.well-known/jwks.json", issuer);
 
         self.route(
             "/.well-known/openid-configuration",
             OidcConfigHandler { issuer, jwks_uri },
         )
-        .route("/.well-known/jwks.json", OidcJwksHandler { signer })
+        .route("/.well-known/jwks.json", OidcJwksHandler { signers })
     }
 }

examples/cf-workers/src/lib.rs

@@ -75,7 +75,7 @@ async fn fetch(req: web_sys::Request, env: Env, _ctx: Context) -> Result<web_sys
     // Build router with OIDC discovery (if configured) and STS.
     let mut router = Router::new();
     if let (Some(signer), Some(issuer)) = (oidc_signer, oidc_issuer) {
-        router = router.with_oidc_discovery(issuer, signer);
+        router = router.with_oidc_discovery(issuer, vec![signer]);
     }
     router = router.with_sts(sts_creds, jwks_cache, token_key.clone());
 

examples/lambda/src/main.rs

@@ -93,7 +93,7 @@ async fn main() -> Result<(), Error> {
     // Build router with OIDC discovery (if configured) and STS.
     let mut router = Router::new();
     if let (Some(signer), Some(issuer)) = (oidc_signer, oidc_issuer) {
-        router = router.with_oidc_discovery(issuer, signer);
+        router = router.with_oidc_discovery(issuer, vec![signer]);
     }
     router = router.with_sts(sts_creds, jwks_cache, token_key.clone());
 

examples/server/src/server.rs

@@ -113,7 +113,7 @@ where
     // Build router with OIDC discovery (if configured) and STS.
     let mut proxy_router = ProxyRouter::new();
     if let (Some(signer), Some(issuer)) = (oidc_signer, oidc_issuer) {
-        proxy_router = proxy_router.with_oidc_discovery(issuer, signer);
+        proxy_router = proxy_router.with_oidc_discovery(issuer, vec![signer]);
     }
     proxy_router = proxy_router.with_sts(sts_creds, jwks_cache, token_key.clone());