[grid] fix Global Account frontend auth sample

[DhruvPareek]

Summary

• UTF-8 encode the Grid passkey reauth challenge before passing it to navigator.credentials.get(), instead of base64url-decoding it.
• Build Grid-Wallet-Signature as the Turnkey API-key stamp shape Grid expects: base64url JSON with publicKey, scheme, and DER signature hex.
• Remove the obsolete raw base64 signature helper from the sample.

Validation

• npm run build in samples/frontend
• make build at the stack tip

[vercel]

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
grid-flow-builder	Ignored	Preview	Jun 10, 2026 5:08pm

[DhruvPareek]

• [grid] fix Global Account sandbox docs #567
• [grid] fix Global Account auth snippets #566
• [grid] fix passkey registration samples #565
• [grid] fix Global Account HPKE docs #564
• [grid] fix Global Account frontend auth sample #563 👈 (View in Graphite)
• [grid] clarify email OTP registration bundle docs #562
• [grid] fix passkey reauth challenge docs #561
• main

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[greptile-apps]

Greptile Summary

This PR fixes two correctness issues in the Global Account frontend authentication sample for the real (non-sandbox) passkey reauth flow.

• Challenge encoding: replaces base64urlToBytes(challenge.challenge) with new TextEncoder().encode(challenge.challenge), aligning with how Grid's /challenge endpoint actually sends the challenge string.
• Wallet signature format: replaces the old raw base64-encoded DER signature with a Turnkey API-key stamp — base64url-encoded JSON containing publicKey, scheme, and signature — matching what Grid's Grid-Wallet-Signature header expects.
• Removes the now-unused base64urlToBytes and bytesToBase64 helpers.

Confidence Score: 5/5

Safe to merge — both changes are correctness fixes to the production signing path in a sample file, and the sandbox path (the default) is untouched.

The two changes (challenge encoding and stamp format) are targeted and internally consistent. The removed helpers are genuinely unused after the change, and the remaining utility functions are still present and used correctly.

No files require special attention.

Important Files Changed

Filename	Overview
samples/frontend/src/steps/embeddedWallet/AuthenticateAndSign.tsx	Fixes WebAuthn challenge encoding and replaces raw base64 DER signature output with a Turnkey API-key stamp; removes two now-unused helpers. Changes are self-consistent and sandbox path is unaffected.

_{Reviews (2): Last reviewed commit: "[grid] fix Global Account frontend auth ..." | Re-trigger Greptile}

[DhruvPareek]

Merge activity

• Jun 10, 6:25 PM UTC: @DhruvPareek merged this pull request with Graphite.