Summary  
This chapter demonstrates how to implement sign-in functionality by validating credentials with Zod, fetching user records from a database, and verifying password hashes with bcrypt in an authentication provider.

General domain of usage  
Web application authentication

### 1. Handling Authentication Logic
In the `auth.ts` file, use the `authorize` function to manage the authentication logic. Validate the email and password using `zod` before checking if the user exists in the database.

### 2. Fetching User from Database
After validating credentials, create a `getUser` function that queries the user from the database using Postgres.

### 3. Checking Passwords Match
Call `bcrypt.compare` to check if the entered password matches the one stored in the database.

Learn to build modern, high-performance web applications using Next.js. Set up projects with structured layouts, styling, and routing for seamless navigation. Fetch and display data efficiently while optimizing rendering and performance. Implement advanced features like pagination, CRUD operations, and global search for dynamic web apps. Deploy your Next.js projects and connect them with databases, and add authentication to protect user data.

Let's discuss what you need to learn before diving into the Next.js framework, what to expect from this course, and what you'll build.

We will set up the project, inspect ways to add styling to our app and cover visual aspects such as images, fonts, pages, and layouts.

Learn how to easily create and manage a new view for your app and navigate through all pages seamlessly with an incorporated routing system.

Deploy the Next.js app using GitHub and Vercel accounts. Additionally, establish a database to supply the app with the necessary data.

Consider how to obtain and show data to the user clearly and efficiently.

Discover how to implement modern web features such as pagination, CRUD operations, global search, form validation, and more.

Authentication implementation in Next.js.

Implementing Sign-In Functionality

Back to the Project

1. Handling Authentication Logic

2. Fetching User from Database

3. Checking Passwords Match

In Practice