This is a long and detailed technical blog post about building user signup and login functionality without external dependencies, focusing on security best practices. Here's a paraphrased and slightly shortened version, maintaining the original meaning and image placement:

User Signup & Login in a Node.js Application (Part 3)

This blog post continues a series on building a Twitter-clone application using Node.js, focusing on implementing user signup and login without relying on external email services or other dependencies. The core authentication logic is encapsulated in an Auth class, which handles user creation and verification.

The Auth class uses a Pass class for password hashing, employing the scrypt algorithm for security. This avoids external dependencies while providing robust password protection. The Pass class includes methods for hashing passwords and verifying password inputs against stored hashes. The system includes error handling for various scenarios, such as user existence and incorrect passwords. While OWASP guidelines suggest avoiding explicit error messages revealing username existence, this implementation prioritizes user experience by providing informative error messages.

The application's routing (App class) handles GET and POST requests for signup and login. Successful signup and login redirect the user to a profile page, using cookies to manage user sessions. Cookies are signed using HMAC with a secret key to prevent tampering. The parseCookies function handles both parsing and verification of signed cookies.

The profile page (GET /profile) displays a personalized greeting using the username from the verified cookie. If the cookie is missing or invalid, the user is redirected to the login page.

The complete code examples and tests are provided in the original blog post, demonstrating the implementation of the Auth, Pass, and App classes, along with the cookie handling functions. The use of JSDoc for type hinting enhances code readability and maintainability. The blog post emphasizes a test-driven development (TDD) approach, showcasing the creation of tests before implementing the corresponding functionality.

The blog concludes with a functional signup and login system, secure cookie handling, and a basic profile page, all built without external dependencies. Further improvements, such as more robust error handling and more comprehensive testing, are suggested for a production-ready application.

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