Two-factor authentication refers to a pattern of users needing both something they know, like a password, and something they have, like a verification token from a mobile device.

This tutorial will cover how to implement a verification token system with the Vonage Verify API and Express.js.

The application will have three pages. An initial page that asks for a mobile number, a page where users provide the code sent to them, and finally, a page which they'll see if their code was correct and the verification successful.

The finished code example is available at https://github.com/nexmo-community/verify-node-express

Prerequisites

• Node.js installed on your machine

Set Up

Create a new directory and open it in a terminal. Run npm init -y to create a package.json file and install dependencies with npm install express body-parser nunjucks nexmo.

Create an index.js file and set up the dependencies:

const app = require('express')()
const bodyParser = require('body-parser')
const nunjucks = require('nunjucks')
const Nexmo = require('nexmo')

app.use(bodyParser.json())
app.use(bodyParser.urlencoded({ extended: false }))
nunjucks.configure('views', { express: app })

const nexmo = new Nexmo({ 
  apiKey: 'API KEY FROM DASHBOARD',
  apiSecret: 'API SECRET FROM DASHBOARD'
})

// Other code will go here

app.listen(3000)

Nunjucks allows data to be passed to templates using the {{ variable }} syntax. It is set up to automatically parse files in the views directory and is linked with the express application stored in app.

Create the Landing Page

Create a directory called views and an index.html file inside of it with the following content:

{{ message }}

<form method="post" action="verify">
  <input name="number" type="tel">
  <button>Get code</button>
</form>

Create a route in index.js to render this view:

app.get('/', (req, res) => { 
  res.render('index.html', { message: 'Hello, world!' }) 
})

Run node index.js in your terminal and open localhost:3000 in your browser. Notice that the message is populated at the top of the page in place of the {{ message }} in the code.

Create a Verification Request

The form on index.html will send a POST request to /verify when submitted. Create a new route to handle this in index.js:

app.post('/verify', (req, res) => {
  nexmo.verify.request({
    number: req.body.number,
    brand: 'ACME Corp'
  }, (error, result) => {
    if(result.status != 0) {
      res.render('index.html', { message: result.error_text })
    } else {
      res.render('check.html', { requestId: result.request_id })
    }
  })
})

By default, workflow 1 is used, which sends an SMS, then calls to read out a code , and then another call. The final step will wait 5 minutes before the whole request expires. You can pass workflow_id as an option if you want to change this behavior.

The result will contain a status property - 0 means the action has been successful, and anything else means there has been an error - which is passed to the rendered index.html page. If successful check.html is rendered.

Check the Code

Create check.html in the views directory:

<form method="post" action="check">
  <input name="code" placeholder="Enter code">
  <input name="requestId" type="hidden" value="{{ requestId }}">
  <button>Verify</button>
</form>

As well as the code, the request ID is required to check if the code is correct. Using the same method as {{message}}, the value of the hidden field requestId is provided dynamically.

Like before, this will submit a POST request to the /check endpoint as this is provided in the action attribute.

Create a new endpoint in index.js:

app.post('/check', (req, res) => {
  nexmo.verify.check({
    request_id: req.body.requestId,
    code: req.body.code
  }, (error, result) => {
    if(result.status != 0) {
      res.render('index.html', { message: result.error_text })
    } else {
      res.render('success.html')
    }
  })
})

If the returned status is 0, the check has been successful and the verification is complete. Create a success.html file in the views folder to celebrate:

<h1>🎉 Success! 🎉</h1>

What Next?

Congratulations on implementing 2FA. Hopefully, you'll agree that it was an enjoyable experience.

In production, there are some additional considerations you'll want to factor in:

• More robust handling of errors and non-zero status codes.
• Providing the ability to cancel ongoing verifications.
• Allowing users to indicate their preference between SMS and call-based code delivery.
• Use the Vonage Number Insight API to ensure only valid phone numbers are passed to the Verify API.

You can find the final project at https://github.com/nexmo-community/verify-node-express

As ever, if you need any support feel free to reach out in the Vonage Developer Community Slack. We hope to see you there.