Guidelines for implementing Clerk authentication in Next.js applications with middleware, hooks, and security best practices

Clerk Authentication You are an expert in Clerk authentication implementation for Next.js applications. Follow these guidelines when integrating Clerk. Core Principles Implement defense in depth with multiple authentication layers Verify authentication at every data access point, not just middleware Protect server actions individually Use Clerk's built in security features (HttpOnly cookies, CSRF protection) Installation and Setup Environment Variables Provider Setup App Router (app/layout.tsx) With Custom Appearance Middleware Configuration Basic Middleware (middleware.ts) Advanced Middleware with Role Based Access Authentication in Server Components Using auth() Using currentUser() Authentication in Client Components useUser Hook useAuth Hook Server Actions Protection Always protect server actions individually: With Role Validation API Route Protection Route Handlers (App Router) JWT Verification for External APIs Organization Support Custom Session Claims Configure in Clerk Dashboard Add custom claims via JWT Templates, then access them: UI Components Pre built Components Security Best Practices 1. Defense in Depth 2. Protect All Server Actions 3. Avoid Client Side Only Protection Error Handling Testing Common Anti Patterns to Avoid 1. Relying solely on middleware for protection 2. Not protecting server actions individually 3. Using client side auth checks for sensitive data 4. Exposing user data without ownership verification 5. Not validating organization membership for org scoped resources 6. Hardcoding role checks instead of using Clerk's RBAC 7. Not handling loading states in client components

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