Authentication Integrations

You are an expert in authentication for Vercel-deployed applications — covering Clerk (native Vercel Marketplace integration), Better Auth (self-hosted, with data in your own database), Descope, and Auth0 for application sign-in, plus Vercel's own primitives: Sign in with Vercel (OAuth/OIDC provider), Passport (deployment protection with your identity provider), and KMS (managed signing keys).

All Next.js examples target Next.js 16, where the request-interception file is proxy.ts (exporting proxy). On Next.js 15 or earlier the same code lives in middleware.ts (exporting middleware).

Clerk (Recommended — Native Marketplace Integration)

Clerk is a native Vercel Marketplace integration with auto-provisioned environment variables and unified billing. Current SDK: @clerk/nextjs v7 (Core 3, March 2026).

Install via Marketplace

# Install Clerk from Vercel Marketplace (auto-provisions env vars)
vercel integration add clerk

Auto-provisioned environment variables:

• CLERK_SECRET_KEY — server-side API key
• NEXT_PUBLIC_CLERK_PUBLISHABLE_KEY — client-side publishable key

SDK Setup

# Install the Clerk Next.js SDK
npm install @clerk/nextjs

Proxy Configuration

// proxy.ts (Next.js 16; middleware.ts on Next.js 15 and earlier)
import { clerkMiddleware } from "@clerk/nextjs/server";

export default clerkMiddleware();

export const config = {
  matcher: [
    // Skip Next.js internals and static files
    "/((?!_next|[^?]*\\.(?:html?|css|js(?!on)|jpe?g|webp|png|gif|svg|ttf|woff2?|ico|csv|docx?|xlsx?|zip|webmanifest)).*)",
    // Always run for API routes
    "/(api|trpc)(.*)",
  ],
};

Protect Routes

// proxy.ts — protect specific routes
import { clerkMiddleware, createRouteMatcher } from "@clerk/nextjs/server";

const isProtectedRoute = createRouteMatcher(["/dashboard(.*)", "/api(.*)"]);

export default clerkMiddleware(async (auth, req) => {
  if (isProtectedRoute(req)) {
    await auth.protect();
  }
});

Frontend API Proxy (Core 3)

Proxy Clerk's Frontend API through your own domain to avoid third-party requests:

// proxy.ts
export default clerkMiddleware({
  frontendApiProxy: { enabled: true },
});

Provider Setup

// app/layout.tsx
import { ClerkProvider } from "@clerk/nextjs";

export default function RootLayout({
  children,
}: {
  children: React.ReactNode;
}) {
  return (
    <html lang="en">
      <body>
        <ClerkProvider>{children}</ClerkProvider>
      </body>
    </html>
  );
}

Sign-In and Sign-Up Pages

// app/sign-in/[[...sign-in]]/page.tsx
import { SignIn } from "@clerk/nextjs";

export default function Page() {
  return <SignIn />;
}

// app/sign-up/[[...sign-up]]/page.tsx
import { SignUp } from "@clerk/nextjs";

export default function Page() {
  return <SignUp />;
}

Add routing env vars to .env.local:

NEXT_PUBLIC_CLERK_SIGN_IN_URL=/sign-in
NEXT_PUBLIC_CLERK_SIGN_UP_URL=/sign-up

Access User Data

// Server component
import { currentUser } from "@clerk/nextjs/server";

export default async function Page() {
  const user = await currentUser();
  return <p>Hello, {user?.firstName}</p>;
}

// Client component
"use client";
import { useUser } from "@clerk/nextjs";

export default function UserGreeting() {
  const { user, isLoaded } = useUser();
  if (!isLoaded) return null;
  return <p>Hello, {user?.firstName}</p>;
}

API Route Protection

// app/api/protected/route.ts
import { auth } from "@clerk/nextjs/server";

export async function GET() {
  const { userId } = await auth();
  if (!userId) {
    return Response.json({ error: "Unauthorized" }, { status: 401 });
  }
  return Response.json({ userId });
}

Better Auth (Self-Hosted)

Better Auth is a framework-agnostic TypeScript auth library that runs inside your app. Users, sessions, and accounts live in your own database, so the only external dependency is the database itself. Choose it when the user wants auth inside their app with data in their own database, or is building on a framework other than Next.js. Current release line: v1.7.

Agent Workflow

1. Detect framework (Next.js App/Pages Router, SvelteKit, Nuxt, Hono…), database/ORM (prisma/schema.prisma, drizzle.config.ts, pg, @neondatabase/serverless), and package manager from the lockfile.
2. Install better-auth plus the DB driver. Provision Postgres from the Marketplace if the project has no database.
3. Create lib/auth.ts (server) and lib/auth-client.ts (client).
4. Mount the route handler at app/api/auth/[...all]/route.ts.
5. Migrate with npx auth@latest migrate (built-in adapter) or generate + the ORM's migrate (Prisma/Drizzle).
6. Protect routes: cookie check in proxy.ts, real getSession() in pages/route handlers.
7. Verify GET /api/auth/ok returns { "status": "ok" }, then run a sign-up → sign-in → getSession() pass.
8. Re-run migrate after every plugin change.

Install

npm install better-auth pg
# Postgres from the Marketplace (auto-provisions DATABASE_URL)
vercel integration add neon

Environment Variables

BETTER_AUTH_SECRET=<openssl rand -base64 32>
BETTER_AUTH_URL=http://localhost:3000

• Production: set BETTER_AUTH_URL to your production domain.
• Preview: leave BETTER_AUTH_URL unset for the Preview environment. Better Auth infers the base URL from the incoming request, so every preview URL works without config. VERCEL_URL is not read automatically.
• OAuth providers need registered redirect URIs (<base>/api/auth/callback/<provider>), so social login on previews needs a stable branch alias.

Server Config

// lib/auth.ts
import { betterAuth } from "better-auth";
import { nextCookies } from "better-auth/next-js";
import { Pool } from "pg";

export const auth = betterAuth({
  database: new Pool({ connectionString: process.env.DATABASE_URL }),
  emailAndPassword: { enabled: true },
  socialProviders: {
    github: {
      clientId: process.env.GITHUB_CLIENT_ID!,
      clientSecret: process.env.GITHUB_CLIENT_SECRET!,
    },
    // Sign in with Vercel — create a Vercel App in the dashboard for credentials
    vercel: {
      clientId: process.env.VERCEL_CLIENT_ID!,
      clientSecret: process.env.VERCEL_CLIENT_SECRET!,
    },
  },
  session: {
    // Signed cookie cache: most getSession() calls skip the database
    cookieCache: { enabled: true, maxAge: 5 * 60 },
  },
  plugins: [nextCookies()], // keep last — sets cookies from Server Actions
});

Prisma / Drizzle / MongoDB users pass an adapter instead of a pool: prismaAdapter(prisma, { provider: "postgresql" }) from better-auth/adapters/prisma, drizzleAdapter(db, { provider: "pg" }) from better-auth/adapters/drizzle.

Route Handler

// app/api/auth/[...all]/route.ts
import { auth } from "@/lib/auth";
import { toNextJsHandler } from "better-auth/next-js";

export const { GET, POST } = toNextJsHandler(auth);

Database Schema

npx auth@latest migrate    # built-in adapter (pg / mysql / sqlite): applies directly
npx auth@latest generate   # Prisma / Drizzle: writes the schema, then run your ORM's migrate

Re-run after adding or removing plugins. Verify with GET /api/auth/ok → { "status": "ok" }.

Client

// lib/auth-client.ts
import { createAuthClient } from "better-auth/react";

export const authClient = createAuthClient();

"use client";
import { authClient } from "@/lib/auth-client";

// Sign in
await authClient.signIn.email({ email, password, callbackURL: "/dashboard" });
await authClient.signIn.social({ provider: "github", callbackURL: "/dashboard" });
await authClient.signUp.email({ email, password, name });
await authClient.signOut();

// Reactive session
const { data: session, isPending } = authClient.useSession();

Access Session Data (Server)

// Server Component, Server Action, or Route Handler
import { auth } from "@/lib/auth";
import { headers } from "next/headers";
import { redirect } from "next/navigation";

export default async function Page() {
  const session = await auth.api.getSession({ headers: await headers() });
  if (!session) redirect("/sign-in");
  return <p>Hello, {session.user.name}</p>;
}

Every endpoint (including plugin endpoints) is callable server-side via auth.api.* — no HTTP round-trip.

Protect Routes

Only check for the session cookie in middleware/proxy — never call the database there. Do the real check in the page or route handler.

// proxy.ts (Next.js 16) — rename to middleware.ts on Next.js 15
import { NextRequest, NextResponse } from "next/server";
import { getSessionCookie } from "better-auth/cookies";

export function proxy(request: NextRequest) {
  if (!getSessionCookie(request)) {
    return NextResponse.redirect(new URL("/sign-in", request.url));
  }
  return NextResponse.next();
}

export const config = { matcher: ["/dashboard/:path*"] };

Keep It Fast on Vercel

• Cookie cache on (session.cookieCache) — avoids a DB read per request in Fluid Compute functions.
• Redis for shared state — vercel integration add upstash, then pass a secondaryStorage adapter. Sessions and rate-limit counters move to Redis; the default in-memory rate limiter does not share state across function instances. Set rateLimit.storage: "secondary-storage".
• Import plugins from subpaths for tree-shaking: import { twoFactor } from "better-auth/plugins/two-factor", not "better-auth/plugins".
• Cookie check only in middleware — getSessionCookie() is synchronous and works on the Edge runtime; auth.api.getSession() in middleware requires the Node.js runtime and costs a DB hit per request.
• Separate frontend origin? Add it to trustedOrigins (wildcards allowed: "https://*.vercel.app"). Same-origin apps need nothing.

Common Mistakes

Plugins

Server plugin + matching client plugin + re-run migrations.

Agent Tooling

Install the official Better Auth skills for deeper, version-aware guidance (planning questionnaire, adapters, migrations, best practices):

npx skills add better-auth/skills

Docs are versioned. Match the better-auth version in the lockfile, then start from better-auth.com/llms.txt or the docs MCP server (https://mcp.better-auth.com/mcp, or npx auth@latest mcp --cursor to register it).

Descope

Descope is available on the Vercel Marketplace with native integration support.

Install via Marketplace

vercel integration add descope

SDK Setup

npm install @descope/nextjs-sdk

Provider and Proxy

// app/layout.tsx
import { AuthProvider } from "@descope/nextjs-sdk";

export default function RootLayout({
  children,
}: {
  children: React.ReactNode;
}) {
  return (
    <AuthProvider projectId={process.env.NEXT_PUBLIC_DESCOPE_PROJECT_ID!}>
      <html lang="en">
        <body>{children}</body>
      </html>
    </AuthProvider>
  );
}

// proxy.ts
import { authMiddleware } from "@descope/nextjs-sdk/server";

export default authMiddleware({
  projectId: process.env.DESCOPE_PROJECT_ID!,
  publicRoutes: ["/", "/sign-in"],
});

Sign-In Flow

"use client";
import { Descope } from "@descope/nextjs-sdk";

export default function SignInPage() {
  return <Descope flowId="sign-up-or-in" />;
}

Auth0

Auth0 provides a mature authentication platform with extensive identity provider support.

SDK Setup

npm install @auth0/nextjs-auth0

Configuration

// lib/auth0.ts
import { Auth0Client } from "@auth0/nextjs-auth0/server";

export const auth0 = new Auth0Client();

Required environment variables:

AUTH0_SECRET=<random-secret>
APP_BASE_URL=http://localhost:3000   # optional: omit on Vercel previews and the SDK infers it from the request host
AUTH0_DOMAIN=your-tenant.auth0.com
AUTH0_CLIENT_ID=<client-id>
AUTH0_CLIENT_SECRET=<client-secret>

Proxy

// proxy.ts
import { auth0 } from "@/lib/auth0";
import type { NextRequest } from "next/server";

export async function proxy(request: NextRequest) {
  return await auth0.middleware(request);
}

export const config = {
  matcher: [
    "/((?!_next/static|_next/image|favicon.ico|sitemap.xml|robots.txt).*)",
  ],
};

Access Session Data

// Server component
import { auth0 } from "@/lib/auth0";

export default async function Page() {
  const session = await auth0.getSession();
  return session ? (
    <p>Hello, {session.user.name}</p>
  ) : (
    <a href="/auth/login">Log in</a>
  );
}

Vercel-Native Identity Primitives

These are not replacements for Clerk, Descope, or Auth0. They cover cases where the identity comes from Vercel itself or where you need Vercel to hold the keys.

Sign in with Vercel

Let users log in with their Vercel account. Vercel's Identity Provider implements OAuth 2.0 and OpenID Connect: register an App in the dashboard, redirect to https://vercel.com/oauth/authorize with PKCE (code_challenge_method: 'S256'), state, and nonce, then exchange the code at https://api.vercel.com/login/oauth/token. Access tokens last 1 hour; refresh tokens last 30 days and rotate on use. Never hand-roll the token exchange without PKCE, state, and nonce checks. Docs: https://vercel.com/docs/sign-in-with-vercel/getting-started

Vercel Passport (deployment protection)

Passport protects whole deployments behind your own OIDC identity provider (Okta, Microsoft Entra ID, Auth0, or any OIDC-compatible provider). Vercel Connect stores the OAuth application configuration, and Vercel redirects unauthenticated visitors before any request reaches your code. Use it for internal tools and previews instead of application-level auth. Your app can read the verified visitor identity server-side or verify a forwarded Passport token as a JWT. Enterprise plan; GA since July 2026. Docs: https://vercel.com/docs/passport

Vercel KMS (managed signing keys)

KMS signs JWTs and messages with keys that never leave Vercel. Create an issuer in the team's Key Management settings, install @vercel/kms, and call signJWT({ issuerId, claims, ttl }) (resolves to { token, keyId, algorithm, fingerprint }; @vercel/kms 0.3.0+, signToken is deprecated) inside a route handler or Server Component; the function's OIDC token authorizes the request automatically. Relying parties verify against the published JWKS at https://kms.vercel.com/<issuerId>/jwks.json. Use it instead of storing private signing keys in environment variables. Docs: https://vercel.com/docs/kms

Decision Matrix

Clerk Core 3 Breaking Changes (March 2026)

Clerk provides an upgrade CLI that scans your codebase and applies codemods: npx @clerk/upgrade. Requires Node.js 20.9.0+.

• SignedIn/SignedOut/Protect replaced by Show — e.g. <Protect role="admin"> → <Show when={{ role: 'admin' }}>
• Package renames — @clerk/clerk-react → @clerk/react, @clerk/clerk-expo → @clerk/expo
• ClerkProvider must be inside <body>, not wrapping <html> — the CLI handles this automatically
• @clerk/types removed — import types from the SDK's own /types entry point, or @clerk/shared/types for framework-agnostic code
• Redirect props renamed — afterSignInUrl/afterSignUpUrl/redirectUrl → fallbackRedirectUrl/signUpFallbackRedirectUrl/forceRedirectUrl
• Minimum Next.js version: 15.2.8 (or 16.0.10 on Next.js 16) — later 15.x minors need their patched releases too (15.3.8+, 15.4.10+, 15.5.9+); Next.js 13 and 14 are no longer supported
• Satellite domains — apps no longer auto-redirect on first visit; set satelliteAutoSync: true in middleware and ClerkProvider to restore Core 2 behavior
• getToken() throws ClerkOfflineError when offline — previously returned null; still returns null when signed out

Cross-References

• Marketplace install and env var provisioning → ⤳ skill: marketplace
• Proxy and Routing Middleware patterns → ⤳ skill: routing-middleware
• Accessing protected deployments from CLI or tests → ⤳ skill: access-protected-vercel-deployment
• Environment variable management → ⤳ skill: env-vars
• Neon Postgres / Upstash Redis for Better Auth → ⤳ skill: vercel-storage
• Sign-in through a Vercel Connect connector with Better Auth (@vercel/connect/betterauth); provider API tokens use getToken() → ⤳ skill: vercel-connect

Official Documentation

• Better Auth Docs · Next.js integration · Sign in with Vercel
• Better Auth agent skills
• Clerk + Vercel Marketplace
• Clerk Next.js Quickstart
• Descope Next.js SDK
• Auth0 Next.js SDK
• Sign in with Vercel
• Vercel Passport
• Vercel KMS