Next.js 14 authentication
Tags: nextjs, authjs, authentication, nextauth
Published: 2024-03-05 21:13:53

This is a brief tutorial of how to create an authentication flow in Next.js 14 using NextAuth v5 using the middleware file. These are the steps we are going to follow:

1. **[Creating the project](#creating-the-project)**: Creating a new Next.js project with NextAuth v5.

2. **[Setting up NextAuth](#setting-up-nextauth)**: Configuring NextAuth to use the credentials provider.

3. **[Protecting routes](#protecting-routes)**: Creating a middleware file to protect routes.

### Creating the project

First, we need to create a new [Next.js](https://nextjs.org/docs/getting-started/installation) project. We can do that by running the following command:

```bash
npx create-next-app@latest
```

After that, we need to install NextAuth v5:

```bash
pnpm add next-auth@beta
```

If you face any issues with the installation, you can check the official documentation for [Next.js](https://nextjs.org/docs/getting-started/installation) and [NextAuth](https://authjs.dev/guides/upgrade-to-v5).

### Setting up NextAuth

Next, we need to create a new file called `app/api/auth/[...nextauth]/route.ts` and add the following code:

```ts
export { GET, POST } from "@/auth";
```

Inside `src` folder, create a file called `auth.ts`, where we are going to create a mock function to simulate the access to the database. This is the function that will be called whenever the `signIn` method from NextAuth is called.

```ts
import NextAuth from "next-auth";
import { authConfig } from "./auth.config";
import Credentials from "next-auth/providers/credentials";

async function getUser(email: string, password: string): Promise<any> {
  return {
    id: 1,
    name: "test user",
    email: email,
    password: password,
  };
}

export const {
  auth,
  signIn,
  signOut,
  handlers: { GET, POST },
} = NextAuth({
  ...authConfig,
  providers: [
    Credentials({
      name: "credentials",
      credentials: {
        email: { label: "email", type: "text" },
        password: { label: "password", type: "password" },
      },
      async authorize(credentials) {
        const user = await getUser(
          credentials.email as string,
          credentials.password as string,
        );

        return user ?? null;
      },
    }),
  ],
});
```

Also, create a file called `auth.config.ts` and add the following code:

```ts
import type { NextAuthConfig } from "next-auth";

export const authConfig = {
  session: {
    strategy: "jwt",
  },
  pages: {
    error: "/",
    signIn: "/",
    signOut: "/",
  },
  callbacks: {
    authorized({ auth }) {
      const isAuthenticated = !!auth?.user;

      return isAuthenticated;
    },
  },
  providers: [],
} satisfies NextAuthConfig;
```

Now, we need to define the routes of our application. We are going to create two pages, the root page where all users can access, and the /protected page, where only logged users can access.

First, create a file in `src/lib/routes.ts`. This constants will be used in the middleware verification.

```ts
export const ROOT = "/";
export const PUBLIC_ROUTES = ["/"];
export const DEFAULT_REDIRECT = "/protected";
```

Then, create the two pages, with a `Form` component

```tsx
import Form from "@/components/form";

const Root = () => {
  return (
    <main className="flex items-center justify-center h-screen w-screen">
      <Form />
    </main>
  );
};

export default Root;
```

```tsx
import { auth } from "@/auth";
import { logout } from "@/lib/actions";
import { Button } from "@/components/ui/button";

const Protected = async () => {
  const session = await auth();

  session?.user?.email;

  return (
    <form
      action={logout}
      className="h-screen w-screen flex flex-col justify-center items-center gap-10"
    >
      <div>
        <p className="text-white">{session?.user?.name}</p>
        <p className="text-white">{session?.user?.email}</p>
      </div>
      <Button type="submit" className="w-40" variant="secondary">
        logout
      </Button>
    </form>
  );
};

export default Protected;
```

```tsx
"use client";

import { login } from "@/lib/actions";
import { useFormState } from "react-dom";
import { Input } from "@/components/ui/input";
import { Button } from "@/components/ui/button";

const loginInitialState = {
  message: "",
  errors: {
    email: "",
    password: "",
    credentials: "",
    unknown: "",
  },
};

const Form = () => {
  const [formState, formAction] = useFormState(login, loginInitialState);

  return (
    <form action={formAction} className="space-y-4 w-full max-w-sm">
      <Input required name="email" placeholder="email" />
      <Input required name="password" type="password" placeholder="password" />
      <Button variant="secondary" className="w-full" type="submit">
        submit
      </Button>
    </form>
  );
};

export default Form;
```

We are using zod to validate the our form with the following schema:

```ts
import { z } from "zod";

export const loginSchema = z.object({
  email: z
    .string()
    .trim()
    .min(1, { message: "Email required!" })
    .email({ message: "Invalid email!" }),
  password: z
    .string()
    .trim()
    .min(1, { message: "Password required!" })
    .min(8, { message: "Password must have at least 8 characters!" }),
});
```

Now, we need to create a file called `actions.ts` in `src/lib` folder. This file will contain the server action that will be used in the form.

```ts
"use server";

import { AuthError } from "next-auth";
import { signIn, signOut } from "@/auth";
import { loginSchema } from "@/types/schema";

const defaultValues = {
  email: "",
  password: "",
};

export async function login(prevState: any, formData: FormData) {
  try {
    const email = formData.get("email");
    const password = formData.get("password");

    const validatedFields = loginSchema.safeParse({
      email: email,
      password: password,
    });

    if (!validatedFields.success) {
      return {
        message: "validation error",
        errors: validatedFields.error.flatten().fieldErrors,
      };
    }

    await signIn("credentials", formData);

    return {
      message: "success",
      errors: {},
    };
  } catch (error) {
    if (error instanceof AuthError) {
      switch (error.type) {
        case "CredentialsSignin":
          return {
            message: "credentials error",
            errors: {
              ...defaultValues,
              credentials: "incorrect email or password",
            },
          };
        default:
          return {
            message: "unknown error",
            errors: {
              ...defaultValues,
              unknown: "unknown error",
            },
          };
      }
    }
    throw error;
  }
}

export async function logout() {
  await signOut();
}
```

### Protecting routes

Finally, we need to create a middleware file to protect the routes. Create a file called `middleware.ts` in `src/lib` folder and add the following code:

```ts
import NextAuth from "next-auth";
import { authConfig } from "@/auth.config";
import { DEFAULT_REDIRECT, PUBLIC_ROUTES, ROOT } from "@/lib/routes";

const { auth } = NextAuth(authConfig);

export default auth((req) => {
  const { nextUrl } = req;

  const isAuthenticated = !!req.auth;
  const isPublicRoute = PUBLIC_ROUTES.includes(nextUrl.pathname);

  if (isPublicRoute && isAuthenticated)
    return Response.redirect(new URL(DEFAULT_REDIRECT, nextUrl));

  if (!isAuthenticated && !isPublicRoute)
    return Response.redirect(new URL(ROOT, nextUrl));
});

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

Here, we are retrieving if the user is authenticated for every route in our application and verifying the current path. If the user has a current session and tried to go back to the login page, they will be redirected back to the /protected page. If the user tries to access any route that isn’t public without a session, they will be redirected to the login page. You can use any matcher suitable for your application.

Now, you have a complete authentication flow using middleware in Next.js 14 with NextAuth v5! If you face any problems, you can check the [GitHub repository](https://github.com/renanleonel/next-auth-v5-middleware) with the full code to help you out.