name: clerk-auth description: | Clerk auth with API version 2025-11-10 breaking changes (billing endpoints, payment_source→payment_method), Next.js v6 async auth(), PKCE for custom OAuth, credential stuffing defense. Use when: troubleshooting "Missing Clerk Secret Key", JWKS errors, authorizedParties CSRF, JWT size limits (1.2KB), 431 header errors (Vite dev mode), or testing with 424242 OTP.

Clerk Auth - Breaking Changes & Error Prevention Guide

Package Versions: @clerk/nextjs@6.35.4, @clerk/backend@2.23.2, @clerk/clerk-react@5.56.2, @clerk/testing@1.13.18 Breaking Changes: Nov 2025 - API version 2025-11-10, Oct 2024 - Next.js v6 async auth() Last Updated: 2025-11-22

What's New in v6.35.x & API 2025-11-10 (Nov 2025)

1. API Version 2025-11-10 (Nov 10, 2025) - BREAKING CHANGES ⚠️

Affects: Applications using Clerk Billing/Commerce APIs

Critical Changes:

Endpoint URLs: /commerce/ → /billing/ (30+ endpoints)

GET /v1/commerce/plans → GET /v1/billing/plans
GET /v1/commerce/statements → GET /v1/billing/statements
POST /v1/me/commerce/checkouts → POST /v1/me/billing/checkouts

Field Terminology: payment_source → payment_method

// OLD (deprecated)
{ payment_source_id: "...", payment_source: {...} }

// NEW (required)
{ payment_method_id: "...", payment_method: {...} }

Removed Fields: Plans responses no longer include:
- amount, amount_formatted (use fee.amount instead)
- currency, currency_symbol (use fee objects)
- payer_type (use for_payer_type)
- annual_monthly_amount, annual_amount
Removed Endpoints:
- Invoices endpoint (use statements)
- Products endpoint
Null Handling: Explicit rules - null means "doesn't exist", omitted means "not asserting existence"

Migration: Update SDK to v6.35.0+ which includes support for API version 2025-11-10.

Official Guide: https://clerk.com/docs/guides/development/upgrading/upgrade-guides/2025-11-10

2. Next.js v6 Async auth() (Oct 2024) - BREAKING CHANGE ⚠️

Affects: All Next.js Server Components using auth()

// ❌ OLD (v5 - synchronous)
const { userId } = auth()

// ✅ NEW (v6 - asynchronous)
const { userId } = await auth()

Also affects: auth.protect() is now async in middleware

// ❌ OLD (v5)
auth.protect()

// ✅ NEW (v6)
await auth.protect()

Compatibility: Next.js 15, 16 supported. Static rendering by default.

3. PKCE Support for Custom OAuth (Nov 12, 2025)

Custom OIDC providers and social connections now support PKCE (Proof Key for Code Exchange) for enhanced security in native/mobile applications where client secrets cannot be safely stored.

Use case: Mobile apps, native apps, public clients that can't securely store secrets.

4. Client Trust: Credential Stuffing Defense (Nov 14, 2025)

Automatic secondary authentication when users sign in from unrecognized devices:

Activates for users with valid passwords but no 2FA
No configuration required
Included in all Clerk plans

How it works: Clerk automatically prompts for additional verification (email code, backup code) when detecting sign-in from new device.

5. Next.js 16 Support (Nov 2025)

@clerk/nextjs v6.35.2+ includes cache invalidation improvements for Next.js 16 during sign-out.

Critical Patterns & Error Prevention

Next.js v6: Async auth() Helper

Pattern:

import { auth } from '@clerk/nextjs/server'

export default async function Page() {
  const { userId } = await auth()  // ← Must await

  if (!userId) {
    return <div>Unauthorized</div>
  }

  return <div>User ID: {userId}</div>
}

Cloudflare Workers: authorizedParties (CSRF Prevention)

CRITICAL: Always set authorizedParties to prevent CSRF attacks

import { verifyToken } from '@clerk/backend'

const { data, error } = await verifyToken(token, {
  secretKey: c.env.CLERK_SECRET_KEY,
  // REQUIRED: Prevent CSRF attacks
  authorizedParties: ['https://yourdomain.com'],
})

Why: Without authorizedParties, attackers can use valid tokens from other domains.

Source: https://clerk.com/docs/reference/backend/verify-token

JWT Templates - Size Limits & Shortcodes

JWT Size Limitation: 1.2KB for Custom Claims ⚠️

Problem: Browser cookies limited to 4KB. Clerk's default claims consume ~2.8KB, leaving 1.2KB for custom claims.

⚠️ Development Note: When testing custom JWT claims in Vite dev mode, you may encounter "431 Request Header Fields Too Large" error. This is caused by Clerk's handshake token in the URL exceeding Vite's 8KB limit. See Issue #11 for solution.

Solution:

// ✅ GOOD: Minimal claims
{
  "user_id": "{{user.id}}",
  "email": "{{user.primary_email_address}}",
  "role": "{{user.public_metadata.role}}"
}

// ❌ BAD: Exceeds limit
{
  "bio": "{{user.public_metadata.bio}}",  // 6KB field
  "all_metadata": "{{user.public_metadata}}"  // Entire object
}

Best Practice: Store large data in database, include only identifiers/roles in JWT.

Available Shortcodes Reference

Category	Shortcodes	Example
User ID & Name	`{{user.id}}`, `{{user.first_name}}`, `{{user.last_name}}`, `{{user.full_name}}`	`"John Doe"`
Contact	`{{user.primary_email_address}}`, `{{user.primary_phone_address}}`	`"john@example.com"`
Profile	`{{user.image_url}}`, `{{user.username}}`, `{{user.created_at}}`	`"https://..."`
Verification	`{{user.email_verified}}`, `{{user.phone_number_verified}}`	`true`
Metadata	`{{user.public_metadata}}`, `{{user.public_metadata.FIELD}}`	`{"role": "admin"}`
Organization	`org_id`, `org_slug`, `org_role` (in sessionClaims)	`"org:admin"`

Advanced Features:

String Interpolation: "{{user.last_name}} {{user.first_name}}"
Conditional Fallbacks: "{{user.public_metadata.role || 'user'}}"
Nested Metadata: "{{user.public_metadata.profile.interests}}"

Official Docs: https://clerk.com/docs/guides/sessions/jwt-templates

Testing with Clerk

Test Credentials (Fixed OTP: 424242)

Test Emails (no emails sent, fixed OTP):

john+clerk_test@example.com
jane+clerk_test@gmail.com

Test Phone Numbers (no SMS sent, fixed OTP):

+12015550100
+19735550133

Fixed OTP Code: 424242 (works for all test credentials)

Generate Session Tokens (60-second lifetime)

Script (scripts/generate-session-token.js):

# Generate token
CLERK_SECRET_KEY=sk_test_... node scripts/generate-session-token.js

# Create new test user
CLERK_SECRET_KEY=sk_test_... node scripts/generate-session-token.js --create-user

# Auto-refresh token every 50 seconds
CLERK_SECRET_KEY=sk_test_... node scripts/generate-session-token.js --refresh

Manual Flow:

Create user: POST /v1/users
Create session: POST /v1/sessions
Generate token: POST /v1/sessions/{session_id}/tokens
Use in header: Authorization: Bearer <token>

E2E Testing with Playwright

Install @clerk/testing for automatic Testing Token management:

npm install -D @clerk/testing

Global Setup (global.setup.ts):

import { clerkSetup } from '@clerk/testing/playwright'
import { test as setup } from '@playwright/test'

setup('global setup', async ({}) => {
  await clerkSetup()
})

Test File (auth.spec.ts):

import { setupClerkTestingToken } from '@clerk/testing/playwright'
import { test } from '@playwright/test'

test('sign up', async ({ page }) => {
  await setupClerkTestingToken({ page })

  await page.goto('/sign-up')
  await page.fill('input[name="emailAddress"]', 'test+clerk_test@example.com')
  await page.fill('input[name="password"]', 'TestPassword123!')
  await page.click('button[type="submit"]')

  // Verify with fixed OTP
  await page.fill('input[name="code"]', '424242')
  await page.click('button[type="submit"]')

  await expect(page).toHaveURL('/dashboard')
})

Official Docs: https://clerk.com/docs/guides/development/testing/overview

Known Issues Prevention

This skill prevents 11 documented issues:

Issue #1: Missing Clerk Secret Key

Error: "Missing Clerk Secret Key or API Key" Source: https://stackoverflow.com/questions/77620604 Prevention: Always set in .env.local or via wrangler secret put

Issue #2: API Key → Secret Key Migration

Error: "apiKey is deprecated, use secretKey" Source: https://clerk.com/docs/upgrade-guides/core-2/backend Prevention: Replace apiKey with secretKey in all calls

Issue #3: JWKS Cache Race Condition

Error: "No JWK available" Source: https://github.com/clerk/javascript/blob/main/packages/backend/CHANGELOG.md Prevention: Use @clerk/backend@2.17.2 or later (fixed)

Issue #4: Missing authorizedParties (CSRF)

Error: No error, but CSRF vulnerability Source: https://clerk.com/docs/reference/backend/verify-token Prevention: Always set authorizedParties: ['https://yourdomain.com']

Issue #5: Import Path Changes (Core 2)

Error: "Cannot find module" Source: https://clerk.com/docs/upgrade-guides/core-2/backend Prevention: Update import paths for Core 2

Issue #6: JWT Size Limit Exceeded

Error: Token exceeds size limit Source: https://clerk.com/docs/backend-requests/making/custom-session-token Prevention: Keep custom claims under 1.2KB

Issue #7: Deprecated API Version v1

Error: "API version v1 is deprecated" Source: https://clerk.com/docs/upgrade-guides/core-2/backend Prevention: Use latest SDK versions (API v2025-11-10)

Issue #8: ClerkProvider JSX Component Error

Error: "cannot be used as a JSX component" Source: https://stackoverflow.com/questions/79265537 Prevention: Ensure React 19 compatibility with @clerk/clerk-react@5.56.2+

Issue #9: Async auth() Helper Confusion

Error: "auth() is not a function" Source: https://clerk.com/changelog/2024-10-22-clerk-nextjs-v6 Prevention: Always await: const { userId } = await auth()

Issue #10: Environment Variable Misconfiguration

Error: "Missing Publishable Key" or secret leaked Prevention: Use correct prefixes (NEXT_PUBLIC_, VITE_), never commit secrets

Issue #11: 431 Request Header Fields Too Large (Vite Dev Mode)

Error: "431 Request Header Fields Too Large" when signing in Source: Common in Vite dev mode when testing custom JWT claims Cause: Clerk's __clerk_handshake token in URL exceeds Vite's 8KB header limit Prevention:

Add to package.json:

{
  "scripts": {
    "dev": "NODE_OPTIONS='--max-http-header-size=32768' vite"
  }
}

Temporary Workaround: Clear browser cache, sign out, sign back in

Why: Clerk dev tokens are larger than production; custom JWT claims increase handshake token size

Note: This is different from Issue #6 (session token size). Issue #6 is about cookies (1.2KB), this is about URL parameters in dev mode (8KB → 32KB).

Official Documentation

Clerk Docs: https://clerk.com/docs
Next.js Guide: https://clerk.com/docs/references/nextjs/overview
React Guide: https://clerk.com/docs/references/react/overview
Backend SDK: https://clerk.com/docs/reference/backend/overview
JWT Templates: https://clerk.com/docs/guides/sessions/jwt-templates
API Version 2025-11-10 Upgrade: https://clerk.com/docs/guides/development/upgrading/upgrade-guides/2025-11-10
Testing Guide: https://clerk.com/docs/guides/development/testing/overview
Context7 Library ID: /clerk/clerk-docs

Package Versions

Latest (Nov 22, 2025):

{
  "dependencies": {
    "@clerk/nextjs": "^6.35.4",
    "@clerk/clerk-react": "^5.56.2",
    "@clerk/backend": "^2.23.2",
    "@clerk/testing": "^1.13.18"
  }
}

Token Efficiency:

Without skill: ~5,200 tokens (setup tutorials, JWT templates, testing setup)
With skill: ~2,500 tokens (breaking changes + critical patterns + error prevention)
Savings: ~52% (~2,700 tokens)

Errors prevented: 11 documented issues with exact solutions Key value: API 2025-11-10 breaking changes, Next.js v6 async auth(), PKCE for custom OAuth, credential stuffing defense, JWT size limits, 431 header error workaround

Last verified: 2025-11-22 | Skill version: 2.0.0 | Changes: Added API version 2025-11-10 breaking changes (billing endpoints), PKCE support, Client Trust defense, Next.js 16 support. Removed tutorials (~480 lines). Updated SDK versions. Focused on breaking changes + error prevention + critical patterns.

clerk-auth