clerk-astro-patterns

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_).

Docs

Astro SDK