Clerk Install & Auth Skill

Clerk Install & Auth

Overview

Set up Clerk SDK and configure authentication for Next.js, React, or Express. This skill covers SDK installation, environment variables, ClerkProvider, middleware, and initial auth verification.

Prerequisites

Node.js 18+
Package manager (npm, pnpm, or yarn)
Clerk account at dashboard.clerk.com
Publishable Key (pk_test_*) and Secret Key (sk_test_*) from Clerk Dashboard > API Keys

Instructions

Step 1: Install SDK for Your Framework

set -euo pipefail
# Next.js (App Router or Pages Router)
npm install @clerk/nextjs

# React SPA (Vite, CRA, etc.)
npm install @clerk/clerk-react

# Express / Node.js backend
npm install @clerk/express

# Backend-only (Cloudflare Workers, serverless, etc.)
npm install @clerk/backend

Step 2: Configure Environment Variables

# .env.local — never commit this file
NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY=pk_test_...
CLERK_SECRET_KEY=sk_test_...

# Optional: routing URLs
NEXT_PUBLIC_CLERK_SIGN_IN_URL=/sign-in
NEXT_PUBLIC_CLERK_SIGN_UP_URL=/sign-up
NEXT_PUBLIC_CLERK_AFTER_SIGN_IN_URL=/dashboard
NEXT_PUBLIC_CLERK_AFTER_SIGN_UP_URL=/onboarding

Ensure .env.local is in .gitignore:

echo ".env.local" >> .gitignore

Step 3: Add ClerkProvider (Next.js App Router)

// app/layout.tsx
import { ClerkProvider, SignInButton, SignedIn, SignedOut, UserButton } from '@clerk/nextjs'
import './globals.css'

export default function RootLayout({ children }: { children: React.ReactNode }) {
  return (
    <ClerkProvider>
      <html lang="en">
        <body>
          <header className="flex justify-between p-4">
            <SignedOut>
              <SignInButton />
            </SignedOut>
            <SignedIn>
              <UserButton />
            </SignedIn>
          </header>
          {children}
        </body>
      </html>
    </ClerkProvider>
  )
}

Step 4: Add Middleware

// middleware.ts (project root, NOT inside app/ or src/app/)
import { clerkMiddleware, createRouteMatcher } from '@clerk/nextjs/server'

// Define which routes should be publicly accessible
const isPublicRoute = createRouteMatcher([
  '/',
  '/sign-in(.*)',
  '/sign-up(.*)',
  '/api/webhooks(.*)',
])

export default clerkMiddleware(async (auth, req) => {
  if (!isPublicRoute(req)) {
    await auth.protect()
  }
})

export const config = {
  matcher: [
    // Skip Next.js internals and static files
    '/((?!_next|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest)).*)',
    // Always run for API routes
    '/(api|trpc)(.*)',
  ],
}

Step 5: Create Sign-In and Sign-Up Pages

// app/sign-in/[[...sign-in]]/page.tsx
import { SignIn } from '@clerk/nextjs'

export default function SignInPage() {
  return (
    <div className="flex min-h-screen items-center justify-center">
      <SignIn />
    </div>
  )
}

// app/sign-up/[[...sign-up]]/page.tsx
import { SignUp } from '@clerk/nextjs'

export default function SignUpPage() {
  return (
    <div className="flex min-h-screen items-center justify-center">
      <SignUp />
    </div>
  )
}

Step 6: Verify Connection

// app/api/health/route.ts
import { auth } from '@clerk/nextjs/server'

export async function GET() {
  const { userId } = await auth()
  return Response.json({
    clerkConnected: true,
    authenticated: !!userId,
    userId: userId || null,
  })
}

React SPA Setup (Vite)

// src/main.tsx
import { ClerkProvider } from '@clerk/clerk-react'
import App from './App'

const PUBLISHABLE_KEY = import.meta.env.VITE_CLERK_PUBLISHABLE_KEY

if (!PUBLISHABLE_KEY) {
  throw new Error('Missing VITE_CLERK_PUBLISHABLE_KEY in .env')
}

ReactDOM.createRoot(document.getElementById('root')!).render(
  <ClerkProvider publishableKey={PUBLISHABLE_KEY}>
    <App />
  </ClerkProvider>
)

Express Setup

// server.ts
import express from 'express'
import { clerkMiddleware, requireAuth, getAuth } from '@clerk/express'

const app = express()

// Apply Clerk middleware globally — attaches auth to all requests
app.use(clerkMiddleware())

// Public route
app.get('/api/health', (req, res) => {
  res.json({ status: 'ok' })
})

// Protected route — redirects unauthenticated requests
app.get('/api/profile', requireAuth(), (req, res) => {
  const { userId } = getAuth(req)
  res.json({ userId })
})

app.listen(3001, () => console.log('Server running on :3001'))

Error Handling

| Error | Cause | Solution | |-------|-------|----------| | Missing publishableKey | Env var not set | Add NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY to .env.local | | ClerkProvider must wrap your application | Hook used outside provider | Ensure ClerkProvider wraps root layout | | auth() was called but Clerk can't detect clerkMiddleware() | Middleware not running | Place middleware.ts at project root, check matcher | | Module not found: @clerk/nextjs | Package not installed | Run npm install @clerk/nextjs | | 500 error on all pages | CLERK_SECRET_KEY missing or wrong | Verify key prefix matches environment (sk_test_ for dev) |

Enterprise Considerations

Use separate Clerk instances per environment (dev/staging/prod)
Store keys in platform secrets (Vercel, AWS Secrets Manager), never in .env files committed to git
The CLERK_SECRET_KEY must never be exposed client-side; only NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY is safe for browsers
For monorepos, install @clerk/nextjs only in the app that needs it; use @clerk/backend for shared server packages
Enable Clerk's "Enhanced email deliverability" in production for reliable transactional emails

Resources

Next Steps

Proceed to clerk-hello-world for your first authenticated request.

Agent Skills: Clerk Install & Auth

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