Convert assertion userHandle back to UTF-8 string

This is the opposite of how `user.id` is converted to an ArrayBuffer prior to being passed into `navigator.credentials.create()`, so when this value is returned to the RP in an assertion it will now look like the string value originally specified in attestation options, instead of the base64url-encoded version of that string “for some reason”.

2 files changed, 3 insertions, 2 deletions

diff --git a/packages/browser/src/methods/startAssertion.test.ts b/packages/browser/src/methods/startAssertion.test.ts
index 83c5a8b..a17c160 100644
--- a/packages/browser/src/methods/startAssertion.test.ts
+++ b/packages/browser/src/methods/startAssertion.test.ts
@@ -120,7 +120,7 @@ test('should return base64url-encoded response values', async done => {
   expect(response.response.authenticatorData).toEqual('bW9ja0F1dGhlbnRpY2F0b3JEYXRh');
   expect(response.response.clientDataJSON).toEqual('bW9ja0NsaWVudERhdGFKU09O');
   expect(response.response.signature).toEqual('bW9ja1NpZ25hdHVyZQ');
-  expect(response.response.userHandle).toEqual('bW9ja1VzZXJIYW5kbGU');
+  expect(response.response.userHandle).toEqual('mockUserHandle');
 
   done();
 });
diff --git a/packages/browser/src/methods/startAssertion.ts b/packages/browser/src/methods/startAssertion.ts
index fa25f47..786d55b 100644
--- a/packages/browser/src/methods/startAssertion.ts
+++ b/packages/browser/src/methods/startAssertion.ts
@@ -6,6 +6,7 @@ import {
 
 import bufferToBase64URLString from '../helpers/bufferToBase64URLString';
 import base64URLStringToBuffer from '../helpers/base64URLStringToBuffer';
+import bufferToUTF8String from '../helpers/bufferToUTF8String';
 import supportsWebauthn from '../helpers/supportsWebauthn';
 import toPublicKeyCredentialDescriptor from '../helpers/toPublicKeyCredentialDescriptor';
 
@@ -46,7 +47,7 @@ export default async function startAssertion(
 
   let userHandle = undefined;
   if (response.userHandle) {
-    userHandle = bufferToBase64URLString(response.userHandle);
+    userHandle = bufferToUTF8String(response.userHandle);
   }
 
   // Convert values to base64 to make it easier to send back to the server