We will use an NPM module to generate JWT called jsonwebtoken. Open a new console and write the following command into the wc-backend folder to install the module:

$ npm install jsonwebtoken --save

Once the installation is finished. Open security-api.js, and let's import our library, as follows:

const express = require('express')
const jwt = require('jsonwebtoken')
const api = express.Router()

...

With our dependency imported in our file, let's implement the generateToken function. Apply the following changes:

...
const logIn = (username, password) => {
    if (username == 'admin' && password == 'admin') {        
        let userData = {
            name: "Admin"
        }        
        return generateToken(userData)        
    } else {
        return null
    }    
}

const generateToken = userData => {
   return jwt.sign(userData, "s3cret", { expiresIn: '3h' })
}

...

That's all! Let's understand the code. We call the sign function of the jwt object to create our token. We pass the following information to the function:

• userData: The piece of information we want to tokenize
• secret: A secret value that is used to encrypt and validate the token
• expiration: The expiration date of the token

Now we are ready with the authentication logic. To finish our implementation, we have to make this logic available via our REST Controller.