1 files changed, 59 insertions, 0 deletions
diff --git a/packages/server/src/helpers/parseAuthenticatorData.ts b/packages/server/src/helpers/parseAuthenticatorData.ts
new file mode 100644
index 0000000..a3dd868
--- /dev/null
+++ b/packages/server/src/helpers/parseAuthenticatorData.ts
@@ -0,0 +1,59 @@
+import { ParsedAuthenticatorData } from "@webauthntine/typescript-types";
+
+/**
+ * Make sense of the authData buffer contained in an Attestation
+ */
+export default function parseAuthenticatorData(authData: Buffer): ParsedAuthenticatorData {
+  let intBuffer = authData;
+
+  const rpIdHash = intBuffer.slice(0, 32);
+  intBuffer = intBuffer.slice(32);
+
+  const flagsBuf = intBuffer.slice(0, 1);
+  intBuffer = intBuffer.slice(1);
+
+  const flagsInt = flagsBuf[0];
+
+  const flags = {
+    up: !!(flagsInt & 0x01),
+    uv: !!(flagsInt & 0x04),
+    at: !!(flagsInt & 0x40),
+    ed: !!(flagsInt & 0x80),
+    flagsInt,
+  };
+
+  const counterBuf = intBuffer.slice(0, 4);
+  intBuffer = intBuffer.slice(4);
+
+  const counter = counterBuf.readUInt32BE(0);
+
+  let aaguid: Buffer | undefined = undefined;
+  let credentialID: Buffer | undefined = undefined;
+  let COSEPublicKey: Buffer | undefined = undefined;
+
+  if (flags.at) {
+    aaguid = intBuffer.slice(0, 16);
+    intBuffer = intBuffer.slice(16);
+
+    const credIDLenBuf = intBuffer.slice(0, 2);
+    intBuffer = intBuffer.slice(2);
+
+    const credIDLen = credIDLenBuf.readUInt16BE(0);
+
+    credentialID = intBuffer.slice(0, credIDLen);
+    intBuffer = intBuffer.slice(credIDLen);
+
+    COSEPublicKey = intBuffer;
+  }
+
+  return {
+    rpIdHash,
+    flagsBuf,
+    flags,
+    counter,
+    counterBuf,
+    aaguid,
+    credentialID,
+    COSEPublicKey,
+  };
+}