how-to/index.php

<?php
require_once __DIR__ . '/../credentials.php';

if(isset($_POST['number'])){
    session_start();
    $number = $_POST['number'];
    $code = rand(1000, 9999); // random 4 digit code
    $_SESSION['code'] = $code; // store code for later

    $url = 'https://rest.nexmo.com/sms/json?' . http_build_query(array(
            'api_key' => NEXMO_KEY,
            'api_secret' => NEXMO_SECRET,
            'from' => NEXMO_FROM,
            'to' => $number,
            'text' => 'Your verification code is: ' . $code
        ));

    $ch = curl_init($url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    $result = curl_exec($ch);
    curl_close($ch);

    //some error checking
    $data = json_decode($result, true);
    if(!isset($data['messages'])){
        throw new Exception('Unknown API Response');
    }

    foreach($data['messages'] as $message){
        if(0 != $message['status']){
            throw new Exception('API Error: ' . $message['error-text']);
        }
    }

    //redirect to the confirm page
    header('Location: confirm.php');
    return;
}

//no post, just display the HTML
?>
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <meta name="description" content="">
    <meta name="author" content="">
    <link rel="icon" href="http://nexmo.com/favicon.ico">

    <title>Phone Verification Example</title>

    <!-- Bootstrap core CSS -->
    <link href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css" rel="stylesheet">

    <!-- Custom styles for this template -->
    <link href="signin.css" rel="stylesheet">

    <!-- HTML5 shim and Respond.js IE8 support of HTML5 elements and media queries -->
    <!--[if lt IE 9]>
    <script src="//oss.maxcdn.com/html5shiv/3.7.2/html5shiv.min.js"></script>
    <script src="//oss.maxcdn.com/respond/1.4.2/respond.min.js"></script>
    <![endif]-->

</head>

<body>

<div class="container">

    <form class="form-verify" role="form" method="POST" action="index.php">
        <h2 class="form-verify-heading">Verify Your Phone</h2>
        <input name="number" type="tel" class="form-control" placeholder="Phone number" required autofocus>
        <button class="btn btn-lg btn-primary btn-block" type="submit">Verify</button>
    </form>

</div> <!-- /container -->
</body>
</html>