# Prompt-to-PR: Add Better Auth to a Next.js App

> Full SOP for wiring Better Auth into a Next.js App Router project — sessions, email/password, OAuth, and middleware protection in one pass.

**Type:** Playbook  
**Tools:** Cursor, Claude Code, Codex, Windsurf  
**Stack:** Next.js, TypeScript, PostgreSQL  
**Difficulty:** medium  
**Updated:** 2026-06-08

---

A complete playbook for adding [Better Auth](https://www.better-auth.com/) to an existing Next.js 15 App Router project backed by PostgreSQL. Covers the auth server, route handler, client helper, middleware, and sign-in UI in a single agent run.

## 1. Requirement

Add session-based authentication with email/password and GitHub OAuth. Protect all routes under `/dashboard` via Next.js middleware. Store sessions in the existing PostgreSQL database using Better Auth's built-in Drizzle adapter.

## 2. First Prompt

```txt title="First Prompt"
Add Better Auth to this Next.js 15 App Router project.

Stack: PostgreSQL (Drizzle ORM, schema in src/db/schema.ts), TypeScript, Tailwind.

Tasks:
1. Install `better-auth` and `@better-auth/drizzle`.
2. Create `src/lib/auth.ts` — configure BetterAuth with the Drizzle adapter,
   emailAndPassword plugin, and GitHub socialProvider. Read secrets from
   BETTER_AUTH_SECRET, GITHUB_CLIENT_ID, GITHUB_CLIENT_SECRET env vars.
3. Create `src/app/api/auth/[...all]/route.ts` that re-exports the auth handler
   for GET and POST.
4. Create `src/lib/auth-client.ts` that exports a `createAuthClient()` instance
   for client components.
5. Add Better Auth tables to `src/db/schema.ts` using `auth.api.generateSchema()`.
6. Create `src/middleware.ts` that protects every route under `/dashboard`;
   redirect unauthenticated requests to `/sign-in`.
7. Create `src/app/(auth)/sign-in/page.tsx` — a minimal email/password form and
   a "Continue with GitHub" button using the auth client.
8. Do not touch any existing route or component unless strictly necessary.
```

## 3. Expected File Changes

```txt
package.json                              (better-auth, @better-auth/drizzle)
src/lib/auth.ts                           (new — server auth instance)
src/lib/auth-client.ts                    (new — browser auth client)
src/app/api/auth/[...all]/route.ts        (new — catch-all route handler)
src/db/schema.ts                          (new tables: user, session, account, verification)
src/middleware.ts                         (new — route protection)
src/app/(auth)/sign-in/page.tsx           (new — sign-in UI)
.env.local.example                        (BETTER_AUTH_SECRET, GITHUB_* vars)
```

## 4. Review Checklist

- `BETTER_AUTH_SECRET` is at least 32 random bytes — never hardcoded.
- The catch-all route handler exports both `GET` and `POST`.
- `src/middleware.ts` uses `matcher` to skip `_next/static`, `_next/image`, and `/api/auth`.
- The Drizzle adapter receives the same `db` instance used elsewhere — no second connection.
- `createAuthClient()` in `auth-client.ts` points to the correct `baseURL` (reads `NEXT_PUBLIC_APP_URL`).
- Sign-in page is a Client Component (`"use client"`) — no server-only imports.
- GitHub OAuth callback URL in the GitHub app settings matches `/api/auth/callback/github`.
- New schema tables are added, not replacing, existing tables.

## 5. Test Commands

```bash
# Generate and run the new auth migrations
npx drizzle-kit generate
npx drizzle-kit migrate

# Start dev server
bun dev

# Smoke-test: attempt to hit protected route without a session
curl -I http://localhost:3000/dashboard
# Expect: 307 redirect to /sign-in

# Run any existing test suite
bun test
```

## 6. Common Failures

- **`BETTER_AUTH_SECRET` missing at runtime** — Better Auth throws on startup. Add it to `.env.local`; confirm with `console.log(process.env.BETTER_AUTH_SECRET?.length)` in `auth.ts` (remove after).
- **Double Drizzle connection** — agent creates a second `drizzle()` call inside `auth.ts` instead of importing from `src/db/index.ts`. Causes two connection pools.
- **Middleware matches `/api/auth`** — causes infinite redirect loop. The `matcher` must exclude `/api/auth/(.*)`.
- **Client component imports server-only `auth`** — build error. Only `auth-client.ts` should be imported in Client Components.
- **GitHub callback URL mismatch** — OAuth fails silently. Confirm the GitHub OAuth app callback is `http://localhost:3000/api/auth/callback/github` in dev.

## 7. Fix Prompt

```txt title="Fix Prompt"
The middleware is redirecting /api/auth/* to /sign-in, causing an infinite loop.

Fix src/middleware.ts so the matcher explicitly excludes:
- /api/auth/:path*
- /_next/static/:path*
- /_next/image
- /favicon.ico

Also confirm that auth.ts imports `db` from `src/db/index.ts` rather than
creating a second Drizzle instance.
```

## 8. PR Description

```md title="PR description"
## Auth: Add Better Auth (email/password + GitHub OAuth)

- Installs `better-auth` with Drizzle adapter against the existing PostgreSQL db
- Catch-all `/api/auth/[...all]` route handles all auth requests
- Middleware protects `/dashboard/**`; unauthenticated → `/sign-in`
- New sign-in page with email/password form and GitHub OAuth button
- Four new schema tables (`user`, `session`, `account`, `verification`) via migration

**Env vars required** (see `.env.local.example`):
- `BETTER_AUTH_SECRET` — min 32-byte random string
- `GITHUB_CLIENT_ID` / `GITHUB_CLIENT_SECRET`
- `NEXT_PUBLIC_APP_URL`
```