Skill

clerk-astro-patterns

Name: clerk-astro-patterns
Author: Clerk

implement Clerk auth in Astro apps

Published by Clerk Updated Apr 7

Covers Clerk Astro Authentication Serverless Frontend

Description

Astro patterns with Clerk — middleware, SSR pages, island components, API routes, static vs SSR rendering. Triggers on: astro clerk, clerk astro middleware, astro protected page, clerk island component, astro API route auth, clerk astro SSR.

SKILL.md

Astro Patterns

SDK: @clerk/astro v3+. Requires Astro 4.15+.

What Do You Need?

Task	Reference
Configure middleware	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, createRouteMatcher } from '@clerk/astro/server'

const isProtectedRoute = createRouteMatcher(['/dashboard(.*)'])

export const onRequest = clerkMiddleware((auth, context, next) => {
  if (isProtectedRoute(context.request) && !auth().userId) {
    return auth().redirectToSignIn()
  }
  return next()
})

SSR Page Auth

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

<h1>Dashboard</h1>

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`, `createRouteMatcher`	`@clerk/astro/server`
`useAuth`, `useUser`, `UserButton`	`@clerk/astro/react`
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

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