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Overview

This guide shows how to set up SMS-based two-factor authentication (2FA) using Plivo’s APIs and Node.js. Authentication with a one-time password (OTP) delivered to users via SMS is an effective way to secure your application.

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Set up the demo application

First, clone the 2FA demo repository from GitHub and install the dependencies.
git clone [https://github.com/plivo/2fa-node-demo.git](https://github.com/plivo/2fa-node-demo.git)
cd 2fa-node-demo
npm install
Next, edit config.js. Replace the auth placeholders with your credentials from the Plivo console. Add your Plivo phone number and set the phlo_id to null.

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A review of the code

Here’s a walk-through of the key functions in the demo application.

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Step 1: Generate the OTP

This function generates a random six-digit one-time password.
const code = Math.floor(100000 + Math.random() * 900000);

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Step 2: Send an SMS with the OTP

This function sends an SMS message containing the OTP to the user’s number using Plivo’s Send Message API.
sendVerificationCode_sms(DstNumber, Message) {
    const code = Math.floor(100000 + Math.random() * 900000);
    this.client.messages.create({
        src: this.app_number,
        dst: DstNumber,
        text: Message.replace('__code__', code),
    });
    return code;
}

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Failover: Make a voice call with the OTP

If the user doesn’t receive the SMS, they can request the OTP via a voice call using Plivo’s Make a Call API.
sendVerificationCode_call(DstNumber) {
    const code = Math.floor(100000 + Math.random() * 900000);
    this.client.calls.create(
        this.app_number, // from
        DstNumber, // to
        '[https://twofa-answerurl.herokuapp.com/answer_url/](https://twofa-answerurl.herokuapp.com/answer_url/)' + code // answer_url
    );
    return code;
}

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Step 3: Verify the OTP

This function checks if the OTP entered by the user matches the one stored in Redis.
router.get('/checkcode/:number/:code', function(req, res) {
    const number = (req.params.number);
    const code = (req.params.code);
    redisClient.get(`number:${number}:code`, function(err, originalCode) {
        if (originalCode == code) {
            redisClient.del(`number:${number}:code`);
            res.send(JSON.stringify({
                'status': 'success',
                'message': 'Codes match, number verified'
            }));
        } else {
            res.send(JSON.stringify({
                'status': 'failure',
                'message': 'Codes do not match'
            }));
        }
    });
});

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Test

First, start the Redis server.
redis-server
Then, run the application.
node app.js
Use a tool like ngrok to expose your local server to the internet, then open the ngrok URL in your browser to see the demo app.