Passport Local Strategy Login Example with Express

How Passport Local Strategy works in authentication

Passport Local Strategy is used when you want to authenticate users using a username and password stored in your own database. It works by taking the credentials from a login request, verifying them against stored user data, and then returning a user object if the credentials are valid. Once authentication is successful, Passport moves into the session phase where serializeUser stores the user identifier for later requests.

Login flow using Local Strategy

When a user submits login credentials, Passport’s local strategy intercepts the request and compares the provided username and password with the database records. If the credentials match, the user is considered authenticated, and Passport proceeds to create a session for that user. At this point, serializeUser is triggered to store only the user’s unique identifier in the session instead of the full user object.

How session integration works with Local Strategy

After successful login, the session system takes over. The stored user ID is kept inside the session, and on future requests, deserializeUser uses that ID to fetch the complete user object again. This allows the application to maintain authentication state across multiple routes while keeping the login process secure and efficient.