clerk-astro-patterns

SKILL.md

Astro Patterns

SDK: @clerk/astro v4+. Requires Astro 5+.

What Do You Need?

Task
Reference

Configure middleware (bare clerkMiddleware(), checks per page)
references/middleware.md

Protect SSR pages
references/ssr-pages.md

Use Clerk in island components
references/island-components.md

Auth in API routes
references/api-routes.md

Use Clerk with React in Astro
references/astro-react.md

Mental Model

Astro has two rendering modes per page: SSR and static prerender. Clerk works differently in each:

SSR pages — use Astro.locals.auth() which is populated by the middleware

Static pages (export const prerender = true) — Clerk middleware skips them; use client-side hooks in islands

Islands — React/Vue/Svelte components; use useAuth() and other hooks from @clerk/astro/react

Request → clerkMiddleware() → SSR page → Astro.locals.auth()
                                ↓
                         Island (.client) → useAuth() hook

Setup

astro.config.mjs

import { defineConfig } from 'astro/config'
import clerk from '@clerk/astro'

export default defineConfig({
  integrations: [clerk()],
  output: 'server',
})

src/middleware.ts

import { clerkMiddleware } from '@clerk/astro/server'

export const onRequest = clerkMiddleware()

The middleware populates Astro.locals.auth(). Each page and API route checks for itself. createRouteMatcher was removed in @clerk/astro 4.0 (deprecated in 3.x). Don't add it. Existing uses must move to page and API-route checks before upgrading. See the Astro clerkMiddleware() reference.

SSR Page Auth

---
const { userId, orgId } = Astro.locals.auth()
if (!userId) return Astro.redirect('/sign-in')
---

<h1>Dashboard</h1>

API Route Auth

// src/pages/api/data.ts
import type { APIRoute } from 'astro'

export const GET: APIRoute = ({ locals }) => {
  const { userId } = locals.auth()
  if (!userId) return new Response('Unauthorized', { status: 401 })

  return Response.json({ userId })
}

Common Pitfalls

Symptom
Cause
Fix

Astro.locals.auth is undefined
Missing middleware
Add clerkMiddleware to src/middleware.ts

Auth works in dev but not production
output: 'static' globally
Set output: 'server' or hybrid for protected pages

Static page has no auth
Prerendered pages skip middleware
Use export const prerender = false or move to island

Island not reactive to sign-in
Missing client:load directive
Add client:load to the island component

Import Map

What
Import From

clerkMiddleware, clerkClient
@clerk/astro/server

useAuth, UserButton (no useUser)
@clerk/astro/react

$userStore, $authStore
@clerk/astro/client

Astro components (<SignIn>, etc.)
@clerk/astro/components

Env Variables

# .env
PUBLIC_CLERK_PUBLISHABLE_KEY=pk_...
CLERK_SECRET_KEY=sk_...

Astro uses PUBLIC_ prefix for client-exposed variables (not NEXT_PUBLIC_).

See Also

clerk-setup - Initial Clerk install

clerk-custom-ui - Custom flows & appearance

clerk-orgs - B2B organizations

Docs

Astro SDK