1 files changed, 34 insertions, 0 deletions
diff --git a/packages/server/src/metadata/verifyJWT.ts b/packages/server/src/metadata/verifyJWT.ts
new file mode 100644
index 0000000..d7e64ec
--- /dev/null
+++ b/packages/server/src/metadata/verifyJWT.ts
@@ -0,0 +1,34 @@
+import { convertX509PublicKeyToCOSE } from '../helpers/convertX509PublicKeyToCOSE';
+import { isoBase64URL, isoUint8Array } from '../helpers/iso';
+import { COSEALG, COSEKEYS, isCOSEPublicKeyEC2 } from '../helpers/cose';
+import { verifyEC2 } from '../helpers/iso/isoCrypto/verifyEC2';
+
+/**
+ * Lightweight verification for FIDO MDS JWTs.
+ *
+ * Currently assumes `"alg": "ES256"` in the JWT header, it's what FIDO MDS uses. If this ever
+ * needs to support more JWS algorithms, here's the list of them:
+ *
+ * https://www.rfc-editor.org/rfc/rfc7518.html#section-3.1
+ *
+ * (Pulled from https://www.rfc-editor.org/rfc/rfc7515#section-4.1.1)
+ */
+export async function verifyJWT(jwt: string, leafCert: Uint8Array): Promise<boolean> {
+  const [header, payload, signature] = jwt.split('.');
+
+  const certCOSE = convertX509PublicKeyToCOSE(leafCert);
+
+  if (isCOSEPublicKeyEC2(certCOSE)) {
+    return verifyEC2({
+      data: isoUint8Array.fromUTF8String(`${header}.${payload}`),
+      signature: isoBase64URL.toBuffer(signature),
+      cosePublicKey: certCOSE,
+      shaHashOverride: COSEALG.ES256,
+    });
+  }
+
+  const kty = certCOSE.get(COSEKEYS.kty);
+  throw new Error(
+    `JWT verification with public key of kty ${kty} is not supported by this method`,
+  );
+}