Nextjs supabase auth

Next.js + Supabase Auth Integration

Core Principle

Use @supabase/ssr for all Supabase Auth in Next.js. The deprecated @supabase/auth-helpers-nextjs package must not be used. Handle token refresh in middleware, not in client components. Validate sessions server-side with getUser(), never getSession().

---

Client Setup

Three distinct Supabase clients are required. Each serves a different runtime context.

1. Browser Client

Create lib/supabase/client.ts for Client Components:

import { createBrowserClient } from '@supabase/ssr'

export const createClient = () =>
  createBrowserClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!
  )

Use this client in 'use client' components only. It reads and writes cookies automatically via the browser.

2. Server Client

Create lib/supabase/server.ts for Server Components, Server Actions, and Route Handlers:

import { createServerClient } from '@supabase/ssr'
import { cookies } from 'next/headers'

export const createClient = async () => {
  const cookieStore = await cookies()

  return createServerClient(
    process.env.NEXT_PUBLIC_SUPABASE_URL!,
    process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!,
    {
      cookies: {
        getAll: () => cookieStore.getAll(),
        setAll: (cookiesToSet) => {
          cookiesToSet.forEach(({ name, value, options }) => {
            cookieStore.set(name, value, options)
          })
        },
      },
    }
  )
}

3. Middleware Client

Create lib/supabase/middleware.ts for the Next.js middleware layer:

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

export const updateSession = async (request: NextRequest) => {
  const response = NextResponse.next({ request })

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

  const { data: { user } } = await supabase.auth.getUser()

  // Redirect unauthenticated users to login
  if (!user && !request.nextUrl.pathname.startsWith('/login') &&
      !request.nextUrl.pathname.startsWith('/auth')) {
    return NextResponse.redirect(new URL('/login', request.url))
  }

  // Redirect authenticated users away from login
  if (user && request.nextUrl.pathname.startsWith('/login')) {
    return NextResponse.redirect(new URL('/dashboard', request.url))
  }

  return response
}

This client sets cookies on both the request and response objects. Setting on the request ensures downstream Server Components read the refreshed token. Setting on the response sends the updated cookie to the browser.

---

Auth Middleware

Create middleware.ts at the project root:

import { type NextRequest } from 'next/server'
import { updateSession } from '@/lib/supabase/middleware'

export async function middleware(request: NextRequest) {
  return await updateSession(request)
}

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

Middleware Responsibilities

• Run on every request except static assets.
• Refresh session tokens by calling getUser(), which triggers cookie renewal.
• Redirect unauthenticated users to /login.
• Redirect authenticated users away from /login to /dashboard.

---

Auth Callback Route

Create app/auth/callback/route.ts to handle OAuth and Magic Link redirects:

import { NextResponse } from 'next/server'
import { createClient } from '@/lib/supabase/server'

export async function GET(request: Request) {
  const { searchParams, origin } = new URL(request.url)
  const code = searchParams.get('code')
  const next = searchParams.get('next') ?? '/dashboard'

  if (code) {
    const supabase = await createClient()
    const { error } = await supabase.auth.exchangeCodeForSession(code)
    if (!error) {
      return NextResponse.redirect(`${origin}${next}`)
    }
  }

  return NextResponse.redirect(`${origin}/login?error=auth_callback_failed`)
}

---

Sign In / Sign Up Patterns

Server Actions (Preferred)

Create app/login/actions.ts:

'use server'

import { redirect } from 'next/navigation'
import { createClient } from '@/lib/supabase/server'

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) redirect('/login?error=invalid_credentials')
  redirect('/dashboard')
}

export async function signUp(formData: FormData) {
  const supabase = await createClient()

  const { error } = await supabase.auth.signUp({
    email: formData.get('email') as string,
    password: formData.get('password') as string,
  })

  if (error) redirect('/login?error=signup_failed')
  redirect('/login?message=check_email')
}

Always call redirect() after any auth state change in Server Actions. The redirect terminates the action and prevents stale state.

Client-Side OAuth

For OAuth providers, use the browser client:

'use client'

import { createClient } from '@/lib/supabase/client'

export function OAuthButton() {
  const handleLogin = async () => {
    const supabase = createClient()
    await supabase.auth.signInWithOAuth({
      provider: 'google',
      options: { redirectTo: `${window.location.origin}/auth/callback` },
    })
  }

  return <button onClick={handleLogin}>Sign in with Google</button>
}

---

Protected Routes Pattern

Server Components

Protect pages by checking the user in Server Components:

import { redirect } from 'next/navigation'
import { createClient } from '@/lib/supabase/server'

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

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

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

Use getUser() which validates the JWT with the Supabase Auth server. Never use getSession() in Server Components -- it only reads the JWT locally without validation and can be spoofed.

Layout-Level Protection

Apply auth checks in a layout to protect an entire route group:

// app/(protected)/layout.tsx
import { redirect } from 'next/navigation'
import { createClient } from '@/lib/supabase/server'

export default async function ProtectedLayout({ children }: { children: React.ReactNode }) {
  const supabase = await createClient()
  const { data: { user } } = await supabase.auth.getUser()

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

  return <>{children}</>
}

---

Auth State in Client Components

Create an auth provider for client-side auth state:

'use client'

import { createContext, useContext, useEffect, useState } from 'react'
import { createClient } from '@/lib/supabase/client'
import type { User } from '@supabase/supabase-js'

const AuthContext = createContext<{ user: User | null }>({ user: null })

export function AuthProvider({ children, initialUser }: {
  children: React.ReactNode
  initialUser: User | null
}) {
  const [user, setUser] = useState<User | null>(initialUser)

  useEffect(() => {
    const supabase = createClient()
    const { data: { subscription } } = supabase.auth.onAuthStateChange(
      (_event, session) => setUser(session?.user ?? null)
    )
    return () => subscription.unsubscribe()
  }, [])

  return <AuthContext.Provider value={{ user }}>{children}</AuthContext.Provider>
}

export const useAuth = () => useContext(AuthContext)

Pass initialUser from a Server Component to avoid a loading flash. Wrap the app in root layout.

---

Anti-Patterns

Anti-Pattern	Why It Fails	Correct Approach
getSession() for security checks	Reads JWT locally without validation; can be tampered	Use getUser() which validates with Supabase
Storing auth state in localStorage	Bypasses cookie-based session; breaks SSR	Let @supabase/ssr manage cookies
Skipping token refresh in middleware	Sessions expire silently; users get 401s	Always call getUser() in middleware
Using @supabase/auth-helpers-nextjs	Deprecated; incompatible with App Router patterns	Use @supabase/ssr
Auth in API Routes instead of Server Actions	Adds unnecessary API layer; loses RSC benefits	Use Server Actions for auth mutations
Client-side redirect after Server Action	Creates flash of unauthorized content	Use redirect() inside the Server Action

---

Role-Based Access Control

Combine Supabase Auth with RLS and user metadata to enforce role-based access:

// Server Action to check admin role
export async function requireAdmin() {
  const supabase = await createClient()
  const { data: { user } } = await supabase.auth.getUser()

  if (!user) redirect('/login')
  if (user.app_metadata?.role !== 'admin') redirect('/unauthorized')

  return user
}

Set roles via Supabase Admin API or database triggers -- never from client-side code. Store roles in app_metadata (server-writable only), not user_metadata (client-writable).

RLS Policies with Auth

RLS policies reference the authenticated user automatically:

-- Allow users to read only their own data
CREATE POLICY "Users read own data" ON profiles
  FOR SELECT USING (auth.uid() = id);

-- Allow admins to read all data
CREATE POLICY "Admins read all" ON profiles
  FOR SELECT USING (
    (SELECT raw_app_meta_data->>'role' FROM auth.users WHERE id = auth.uid()) = 'admin'
  );

---

Password Reset Flow

Initiate Reset

'use server'

export async function resetPassword(formData: FormData) {
  const supabase = await createClient()

  const { error } = await supabase.auth.resetPasswordForEmail(
    formData.get('email') as string,
    { redirectTo: `${process.env.NEXT_PUBLIC_SITE_URL}/auth/callback?next=/reset-password` }
  )

  if (error) redirect('/login?error=reset_failed')
  redirect('/login?message=check_email_for_reset')
}

Handle Reset Callback

After the user clicks the email link, they arrive at the callback route with an auth code. The callback exchanges the code for a session, then redirects to the password update form:

// app/reset-password/page.tsx
export default async function ResetPasswordPage() {
  const supabase = await createClient()
  const { data: { user } } = await supabase.auth.getUser()

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

  return <UpdatePasswordForm />
}

---

Environment Variables

Required in .env.local:

NEXT_PUBLIC_SUPABASE_URL=https://your-project.supabase.co
NEXT_PUBLIC_SUPABASE_ANON_KEY=your-anon-key

Both are prefixed with NEXT_PUBLIC_ because the browser client needs them. The anon key is safe to expose -- RLS policies enforce security, not the key.

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Quick Reference

Concern	Location	Client
Token refresh	middleware.ts	Middleware client
OAuth/Magic Link callback	app/auth/callback/route.ts	Server client
Sign in/up mutations	Server Actions	Server client
OAuth initiation	Client Component	Browser client
Route protection (SSR)	Server Component or Layout	Server client
Real-time auth state	Client Component + Provider	Browser client
Security validation	Anywhere server-side	getUser() only

---

Dependencies

Skill	Reason
nextjs-patterns	App Router architecture, Server Components, middleware, Server Actions, route groups, and layouts
supabase-patterns	Supabase client initialization, Auth API surface, Row Level Security integration, and database access patterns
react-best-practices (transitive)	Component architecture, hooks, context, and rendering patterns (via nextjs-patterns)
typescript-pro (transitive)	Type safety, generics, and strict configuration (via nextjs-patterns, supabase-patterns)
postgres-best-practices (transitive)	Database schema design and query patterns underlying RLS (via supabase-patterns)
tailwind-patterns (transitive)	Styling patterns for auth UI components (via nextjs-patterns)

Used By

None -- this is a top-layer integration skill.