2 files changed, 20 insertions, 11 deletions
diff --git a/packages/browser/src/helpers/toPublicKeyCredentialDescriptor.ts b/packages/browser/src/helpers/toPublicKeyCredentialDescriptor.ts
new file mode 100644
index 0000000..ad166a5
--- /dev/null
+++ b/packages/browser/src/helpers/toPublicKeyCredentialDescriptor.ts
@@ -0,0 +1,16 @@
+import base64js from 'base64-js';
+import type { PublicKeyCredentialDescriptorJSON } from '@webauthntine/typescript-types';
+
+export default function toPublicKeyCredentialDescriptor(
+  descriptor: PublicKeyCredentialDescriptorJSON,
+): PublicKeyCredentialDescriptor {
+  // Make sure the Base64'd credential ID length is a multiple of 4 or else toByteArray will throw
+  const { id } = descriptor;
+  const padLength = 4 - (id.length % 4);
+  const paddedId = id.padEnd(id.length + padLength, '=');
+
+  return {
+    ...descriptor,
+    id: base64js.toByteArray(paddedId),
+  };
+}
diff --git a/packages/browser/src/methods/startAssertion.ts b/packages/browser/src/methods/startAssertion.ts
index f504f19..826763a 100644
--- a/packages/browser/src/methods/startAssertion.ts
+++ b/packages/browser/src/methods/startAssertion.ts
@@ -3,11 +3,11 @@ import {
   AuthenticatorAssertionResponseJSON,
   AssertionCredential,
 } from '@webauthntine/typescript-types';
-import base64js from 'base64-js';
 
 import toUint8Array from '../helpers/toUint8Array';
 import toBase64String from '../helpers/toBase64String';
 import supportsWebauthn from '../helpers/supportsWebauthn';
+import toPublicKeyCredentialDescriptor from '../helpers/toPublicKeyCredentialDescriptor';
 
 /**
  * Begin authenticator "login" via WebAuthn assertion
@@ -25,16 +25,9 @@ export default async function startAssertion(
   const publicKey: PublicKeyCredentialRequestOptions = {
     ...requestOptionsJSON.publicKey,
     challenge: toUint8Array(requestOptionsJSON.publicKey.challenge),
-    allowCredentials: requestOptionsJSON.publicKey.allowCredentials.map(cred => {
-      // Make sure the credential ID length is a multiple of 4
-      const padLength = 4 - (cred.id.length % 4);
-      const id = cred.id.padEnd(cred.id.length + padLength, '=');
-
-      return {
-        ...cred,
-        id: base64js.toByteArray(id),
-      };
-    }),
+    allowCredentials: requestOptionsJSON.publicKey.allowCredentials.map(
+      toPublicKeyCredentialDescriptor,
+    ),
   };
 
   // Wait for the user to complete assertion