Credentials Provider

The Credentials provider allows you to handle sign-in with username/password or other credentials. It's particularly useful for testing and for integrating with existing authentication systems.

Setup

1. Add Credentials Provider to Auth.js Configuration

In your auth.ts file, import and add the Credentials provider:

import Credentials from "next-auth/providers/credentials"

export const { handlers, auth, signIn, signOut } = NextAuth({
  providers: [
    // Other providers...
    Credentials({
      // The name to display on the sign-in form
      name: "Credentials",
      // The credentials is used to generate a suitable form on the sign-in page
      credentials: {
        email: { label: "Email", type: "email" },
        password: { label: "Password", type: "password" }
      },
      async authorize(credentials) {
        // Add your own logic here to validate credentials
        // Return null if credentials are invalid
        // Return a user object if credentials are valid
        if (credentials?.email === "test@example.com" && credentials?.password === "password") {
          return {
            id: "1",
            name: "Test User",
            email: "test@example.com",
          };
        }
        return null;
      }
    }),
  ],
  // ...
})

Usage

Sign In with Credentials

To sign in with credentials, redirect the user to the Auth.js sign-in page with the credentials provider:

import { signIn } from "next-auth/react"

// Redirect to the sign-in page with credentials provider
signIn("credentials")

// Or sign in programmatically with credentials
signIn("credentials", {
  email: "test@example.com",
  password: "password",
  redirect: false,
}).then((result) => {
  if (result.ok) {
    // Signed in successfully
    window.location.href = "/dashboard";
  } else {
    // Sign-in failed
    console.error("Sign-in failed:", result.error);
  }
});

Integrating with Existing Authentication Systems

The Credentials provider can be used to integrate with existing authentication systems:

Credentials({
  name: "Existing System",
  credentials: {
    username: { label: "Username", type: "text" },
    password: { label: "Password", type: "password" }
  },
  async authorize(credentials) {
    // Make a request to your authentication API
    const res = await fetch("https://your-api.com/auth", {
      method: "POST",
      body: JSON.stringify(credentials),
      headers: { "Content-Type": "application/json" }
    });
    const user = await res.json();
    
    // If the API returned a user, return it
    if (res.ok && user) {
      return user;
    }
    
    // If the API returned an error, return null
    return null;
  }
}),

Security Considerations

When using the Credentials provider, keep these security considerations in mind:

1. Store Passwords Securely: Never store passwords in plain text. Use a secure hashing algorithm like bcrypt.

2. Implement Rate Limiting: Prevent brute force attacks by implementing rate limiting on sign-in attempts.

3. Use HTTPS: Always use HTTPS to encrypt credentials in transit.

4. Consider Two-Factor Authentication: For additional security, consider implementing two-factor authentication.

Testing with Credentials Provider

The Credentials provider is useful for testing authentication flows:

// In your test file
import { signIn } from "next-auth/react"

// Sign in with test credentials
await signIn("credentials", {
  email: "test@example.com",
  password: "password",
  redirect: false,
});

// Now you can test authenticated functionality

Troubleshooting

Common Issues

1. Session Not Persisting: By default, the Credentials provider uses JWT for session management. Make sure you've configured the session strategy correctly.

2. CSRF Protection: Auth.js includes CSRF protection for form submissions. Make sure you're including the CSRF token in your sign-in requests.

3. Redirect Issues: If you're having issues with redirects, try using redirect: false in the signIn function and handle the redirect manually.

Debugging

To enable debug logging in Auth.js, set the debug option to true:

export const { handlers, auth, signIn, signOut } = NextAuth({
  debug: true,
  // Rest of your configuration
})