Using Twilio SMS to set up two-factor authentication for secure websites

This recipe is similar to the two-factor voice authentication recipe but uses SMS instead and texts the user their one-time password.

Again, two-factor authentication is an important tool to verify your users for various purposes and should be used on sites if you care at all about user security.

Forcing a user to verify their identity using two-factor authentication, in order to do something as simple as changing their password, can help promote trust between both you and your users.

Getting ready

The complete source code for this recipe can be found at Chapter1 /Recipe2.

How to do it...

We're going to build our first Twilio app, a two-factor SMS authentication system. This can be plugged into websites to allow users to get called on a phone and verify that they are who they say they are.

  1. Download the Twilio Helper Library (from https://github.com/twilio/twilio-php/zipball/master) and unzip it.
  2. Upload the Services/ folder to your website.
  3. Upload config.php to your website and make sure the following variables are set: 
    <?php
  $accountsid = '';  //  YOUR TWILIO ACCOUNT SID
  $authtoken = '';  //    YOUR TWILIO AUTH TOKEN
  $fromNumber = '';  //  PHONE NUMBER CALLS WILL COME FROM
?>
  4. We'll set up a file called two-factor-sms.php, which will sit on your web server; this file handles the two-factor authentication. 
    <?php
  session_start();
  include 'Services/Twilio.php';
  include 'config.php';
  include 'functions.php';
  $username = cleanVar('username');
  $password = cleanVar('password');
  $phoneNum = cleanVar('phone_number');
  if( isset($_POST['action']) ){
    if( isset($_POST['username']) &&isset($_POST['phone_number'])){
      $message = user_generate_token($username, $phoneNum,'sms');
  }else if( isset($_POST['username']) &&isset($_POST['password'])){
    $message = user_login($username, $password);
  }
  header("Location: two-factor-sms.php?message=" .urlencode($message));
  exit;
}
?>
<html>
<body>
<p>Please enter a username, and a phone number you can be reached at, we will then send you your one-time password via SMS.</p>
<span id="message">
<?php
  echo cleanVar('message');
  $action = (isset($_SESSION['password'])) ? 'login' : 'token';
?>
</span>
<form id="reset-form"  method="POST" class="center">
<input type="hidden" name="action" value="<?php echo$action; ?>"/>
<p>Username: <input type="text" name="username"id="username" value="<?php echo $_SESSION['username'];?>" /></p>
<?php if (isset($_SESSION['password'])) { ?>
  <p>Password: <input type="password" name="password"id="password" /></p>
<?php } else { ?>
  <p>Phone Number: <input type="text" name="phone_number"id="phone_number" /></p>
  <input type="hidden" name="method" value="sms" checked="checked"/>
<?php } ?>
<p><input type="submit" name="submit" id="submit"value="login!"/></p>
<p>&nbsp;</p>
</form>
</body>
</html>
  5. Finally, we're going to include the same functions.php file we used in the Adding two-factor voice authentication to verify users recipe.

How it works...

In steps 1 and 2, we downloaded and installed the Twilio Helper Library for PHP; this library is the heart of your Twilio-powered apps.

In step 3, we uploaded config.php that contains our authentication information to talk to Twilio's API.

Your user is presented with a form where they enter a username and their phone number. Once they submit the form, it generates a one-time usage password and sends it as a text message to the phone number they entered. They then enter this password in the form on the site to verify that they are who they say they are.

What's the big difference between recipes 1 and 2? Really, it's that one does voice and one does SMS. You could combine these as options if you wanted to so that people can choose between voice or SMS. The biggest key is when you call the function user_generate_token; you specify the method as either calls or sms.

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