Next.js + Supabase Auth

Expert integration of Supabase Auth with Next.js App Router

Capabilities

• nextjs-auth
• supabase-auth-nextjs
• auth-middleware
• auth-callback

Prerequisites

• Required skills: nextjs-app-router, supabase-backend

Patterns

Supabase Client Setup

Create properly configured Supabase clients for different contexts

When to use: Setting up auth in a Next.js project

// lib/supabase/client.ts (Browser client) 'use client' import { createBrowserClient } from '@supabase/ssr'

export function createClient() { return createBrowserClient( process.env.NEXT_PUBLIC_SUPABASE_URL!, process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY! ) }

// lib/supabase/server.ts (Server client) import { createServerClient } from '@supabase/ssr' import { cookies } from 'next/headers'

export async function createClient() { const cookieStore = await cookies() return createServerClient( process.env.NEXT_PUBLIC_SUPABASE_URL!, process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!, { cookies: { getAll() { return cookieStore.getAll() }, setAll(cookiesToSet) { // This helper is for a Route Handler/Server Action with writable cookies. // In a Server Component use the official read-only client pattern and // refresh sessions in middleware/proxy; do not attempt cookie writes here. cookiesToSet.forEach(({ name, value, options }) => cookieStore.set(name, value, options)) }, }, } ) }

Auth Middleware

Protect routes and refresh sessions in middleware

When to use: You need route protection or session refresh

// middleware.ts import { createServerClient } from '@supabase/ssr' import { NextResponse, type NextRequest } from 'next/server'

export async function middleware(request: NextRequest) { let response = NextResponse.next({ request })

const supabase = createServerClient( process.env.NEXT_PUBLIC_SUPABASE_URL!, process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!, { cookies: { getAll() { return request.cookies.getAll() }, setAll(cookiesToSet) { cookiesToSet.forEach(({ name, value }) => request.cookies.set(name, value)) response = NextResponse.next({ request }) cookiesToSet.forEach(({ name, value, options }) => response.cookies.set(name, value, options)) }, }, } )

// Refresh session if expired const { data: { user } } = await supabase.auth.getUser()

// Protect dashboard routes if (request.nextUrl.pathname.startsWith('/dashboard') && !user) { return NextResponse.redirect(new URL('/login', request.url)) }

return response }

export const config = { matcher: ['/((?!_next/static|_next/image|favicon.ico).*)'], }

Auth Callback Route

Handle OAuth callback and exchange code for session

When to use: Using OAuth providers (Google, GitHub, etc.)

// app/auth/callback/route.ts import { createClient } from '@/lib/supabase/server' import { NextResponse } from 'next/server'

export async function GET(request: Request) { const { searchParams, origin } = new URL(request.url) const code = searchParams.get('code') const candidate = searchParams.get('next') ?? '/' const next = candidate.startsWith('/') && !candidate.startsWith('//') && !candidate.includes('\') ? candidate : '/'

if (code) { const supabase = await createClient() const { error } = await supabase.auth.exchangeCodeForSession(code) if (!error) { return NextResponse.redirect(new URL(next, process.env.APP_ORIGIN!)) // validated trusted deployment origin } }

return NextResponse.redirect(${origin}/auth/error) }

Server Action Auth

Handle auth operations in Server Actions

When to use: Login, logout, or signup from Server Components

// app/actions/auth.ts 'use server' import { createClient } from '@/lib/supabase/server' import { redirect } from 'next/navigation' import { revalidatePath } from 'next/cache'

export async function signIn(formData: FormData) { const supabase = await createClient() const { error } = await supabase.auth.signInWithPassword({ email: formData.get('email') as string, password: formData.get('password') as string, })

if (error) { return { error: error.message } }

revalidatePath('/', 'layout') redirect('/dashboard') }

export async function signOut() { const supabase = await createClient() await supabase.auth.signOut() revalidatePath('/', 'layout') redirect('/') }

Get User in Server Component

Access the authenticated user in Server Components

When to use: Rendering user-specific content server-side

// app/dashboard/page.tsx import { createClient } from '@/lib/supabase/server' import { redirect } from 'next/navigation'

export default async function DashboardPage() { const supabase = await createClient() const { data: { user } } = await supabase.auth.getUser()

if (!user) { redirect('/login') }

return ( <div> <h1>Welcome, {user.email}</h1> </div> ) }

Validation Checks

Using getSession() for Auth Checks

Severity: ERROR

Message: getSession() doesn't verify the JWT. Use getUser() for secure auth checks.

Fix action: Replace getSession() with getUser() for security-critical checks

OAuth Without Callback Route

Severity: ERROR

Message: Using OAuth but missing callback route at app/auth/callback/route.ts

Fix action: Create app/auth/callback/route.ts to handle OAuth redirects

Browser Client in Server Context

Severity: ERROR

Message: Browser client used in server context. Use createServerClient instead.

Fix action: Import and use createServerClient from @supabase/ssr

Protected Routes Without Middleware

Severity: WARNING

Message: No middleware.ts found. Consider adding middleware for route protection.

Fix action: Create middleware.ts to protect routes and refresh sessions

Hardcoded Auth Redirect URL

Severity: WARNING

Message: Hardcoded localhost redirect. Use origin for environment flexibility.

Fix action: Use window.location.origin or process.env.NEXT_PUBLIC_SITE_URL

Auth Call Without Error Handling

Severity: WARNING

Message: Auth operation without error handling. Always check for errors.

Fix action: Destructure { data, error } and handle error case

Auth Action Without Revalidation

Severity: WARNING

Message: Auth action without revalidatePath. Cache may show stale auth state.

Fix action: Add revalidatePath('/', 'layout') after auth operations

Client-Only Route Protection

Severity: WARNING

Message: Client-side route protection shows flash of content. Use middleware.

Fix action: Move protection to middleware.ts for better UX

Collaboration

Delegation Triggers

• database|rls|queries|tables -> supabase-backend (Auth needs database layer)
• route|page|component|layout -> nextjs-app-router (Auth needs Next.js patterns)
• deploy|production|vercel -> vercel-deployment (Auth needs deployment config)
• ui|form|button|design -> frontend (Auth needs UI components)

Full Auth Stack

Skills: nextjs-supabase-auth, supabase-backend, nextjs-app-router, vercel-deployment

Workflow:

1. Database setup (supabase-backend)
2. Auth implementation (nextjs-supabase-auth)
3. Route protection (nextjs-app-router)
4. Deployment config (vercel-deployment)

Protected SaaS

Skills: nextjs-supabase-auth, stripe-integration, supabase-backend

Workflow:

1. User authentication (nextjs-supabase-auth)
2. Customer sync (stripe-integration)
3. Subscription gating (supabase-backend)

Related Skills

Works well with: nextjs-app-router, supabase-backend

When to Use

• User mentions or implies: supabase auth next
• User mentions or implies: authentication next.js
• User mentions or implies: login supabase
• User mentions or implies: auth middleware
• User mentions or implies: protected route
• User mentions or implies: auth callback
• User mentions or implies: session management

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.

These are separate-file fragments, not a complete auth deployment. Configure and validate the trusted APP_ORIGIN, callback allowlist and exact Next.js/Supabase versions first. Server Components cannot write cookies; use the current official context-specific helper rather than suppressing arbitrary refresh failures. Preserve refreshed cookies on returned redirects. Middleware is not the sole authorization layer: validate sessions/claims and tenant/resource permissions on every server data/action path and enforce RLS. Never expose a service-role key to browsers. See Supabase server-side client guidance.