Great! Now that you've added the MONGODB_URI environment variable, your authentication system is ready to connect to your MongoDB database. Let's go through what you need to do next to get everything working properly.

Next Steps to Complete Your Setup

1. Add the remaining environment variables:

   NEXTAUTH_URL=http://localhost:3000 (use your deployment URL in production) NEXTAUTH_SECRET=your_random_secret_key

   You can generate a secure NEXTAUTH_SECRET with:

   openssl rand -base64 32

2. Install required dependencies:

   npm install next-auth @auth/mongodb-adapter mongodb bcrypt # Types for TypeScript npm install -D @types/bcrypt

3. Initialize your MongoDB database:

   • The Auth.js MongoDB adapter will automatically create the necessary collections in your database.
   • The main collections will be: users, accounts, sessions, and verification_tokens.

4. Test the authentication flow:

   • Start your application and navigate to /signup to create a new account
   • Try signing in with your credentials at /signin
   • After signing in, you should be redirected to the dashboard
   • Test the protected routes by trying to access /dashboard without being logged in

Understanding the Authentication Flow

1. Sign-up process:

   • User submits their information through the sign-up form
   • The API route /api/register hashes the password and stores the user in MongoDB
   • User is redirected to the sign-in page

2. Sign-in process:

   • User enters their credentials
   • Auth.js verifies the credentials against the database
   • If valid, a JWT session is created and stored in cookies
   • User is redirected to the dashboard

3. Session management:

   • The session is maintained via a JWT token in an HTTP-only cookie
   • The middleware checks for this token on protected routes
   • The session lasts for 30 days by default (configurable in the Auth.js options)

4. Sign-out process:

   • When the user clicks "Sign out", the signOut() function is called
   • This clears the session cookie and redirects to the home page

Customization Options

You can customize the authentication system in several ways:

1. Session duration: Modify the maxAge value in the Auth.js configuration
2. Additional providers: Add social login providers like Google, GitHub, etc.
3. User profile fields: Extend the user model to include additional fields
4. UI customization: Modify the sign-in and sign-up forms to match your brand

Troubleshooting

If you encounter any issues:

1. Database connection: Ensure your MONGODB_URI is correct and the database is accessible
2. JWT errors: Make sure NEXTAUTH_SECRET is set properly
3. Redirect issues: Check that NEXTAUTH_URL is set to your application's base URL
4. Session problems: Clear your browser cookies and try signing in again

Let me know if you need any clarification or have questions about implementing specific features!