3 files changed, 12 insertions, 3 deletions
diff --git a/packages/browser/src/helpers/toUint8Array.ts b/packages/browser/src/helpers/toUint8Array.ts
new file mode 100644
index 0000000..1e2243f
--- /dev/null
+++ b/packages/browser/src/helpers/toUint8Array.ts
@@ -0,0 +1,7 @@
+/**
+ * A helper method to convert an arbitrary string sent from the server to a Uint8Array the
+ * authenticator will expect.
+ */
+export default function toUint8Array(value: string): Uint8Array {
+  return new TextEncoder().encode(value);
+}
diff --git a/packages/browser/src/methods/startAttestation.test.ts b/packages/browser/src/methods/startAttestation.test.ts
index ad71488..d178609 100644
--- a/packages/browser/src/methods/startAttestation.test.ts
+++ b/packages/browser/src/methods/startAttestation.test.ts
@@ -3,6 +3,7 @@ import {
   PublicKeyCredentialCreationOptionsJSON,
 } from '@simplewebauthn/typescript-types';
 
+import toUint8Array from '../helpers/toUint8Array';
 import supportsWebauthn from '../helpers/supportsWebauthn';
 import bufferToBase64URLString from '../helpers/bufferToBase64URLString';
 
@@ -17,7 +18,7 @@ const mockAttestationObject = 'mockAtte';
 const mockClientDataJSON = 'mockClie';
 
 const goodOpts1: PublicKeyCredentialCreationOptionsJSON = {
-  challenge: bufferToBase64URLString(Buffer.from('fizz', 'ascii')),
+  challenge: bufferToBase64URLString(toUint8Array('fizz')),
   attestation: 'direct',
   pubKeyCredParams: [
     {
@@ -87,7 +88,7 @@ test('should return base64url-encoded response values', async done => {
       return new Promise(resolve => {
         resolve({
           id: 'foobar',
-          rawId: Buffer.from('foobar', 'ascii'),
+          rawId: toUint8Array('foobar'),
           response: {
             attestationObject: Buffer.from(mockAttestationObject, 'ascii'),
             clientDataJSON: Buffer.from(mockClientDataJSON, 'ascii'),
diff --git a/packages/browser/src/methods/startAttestation.ts b/packages/browser/src/methods/startAttestation.ts
index 9594bb9..0b2235d 100644
--- a/packages/browser/src/methods/startAttestation.ts
+++ b/packages/browser/src/methods/startAttestation.ts
@@ -4,6 +4,7 @@ import {
   AttestationCredentialJSON,
 } from '@simplewebauthn/typescript-types';
 
+import toUint8Array from '../helpers/toUint8Array';
 import bufferToBase64URLString from '../helpers/bufferToBase64URLString';
 import base64URLStringToBuffer from '../helpers/base64URLStringToBuffer';
 import supportsWebauthn from '../helpers/supportsWebauthn';
@@ -27,7 +28,7 @@ export default async function startAttestation(
     challenge: base64URLStringToBuffer(creationOptionsJSON.challenge),
     user: {
       ...creationOptionsJSON.user,
-      id: base64URLStringToBuffer(creationOptionsJSON.user.id),
+      id: toUint8Array(creationOptionsJSON.user.id),
     },
     excludeCredentials: creationOptionsJSON.excludeCredentials.map(toPublicKeyCredentialDescriptor),
   };