amp-form implementation of a MailChimp / Email Subscribe post handler.

mailchimp-post.php

<?php
if (!empty($_POST)) {
    header("access-control-allow-credentials:true");
    header("access-control-allow-headers:Content-Type, Content-Length, Accept-Encoding, X-CSRF-Token");
    header("access-control-allow-methods:POST, GET, OPTIONS");
    header("access-control-allow-origin:".$_SERVER['HTTP_ORIGIN']);
    header("access-control-expose-headers:AMP-Access-Control-Allow-Source-Origin");
    // change to represent your site's protocol, either http or https
    header("amp-access-control-allow-source-origin:https://".$_SERVER['HTTP_HOST']);
    header("Content-Type: application/json");
    $email = isset($_POST['email']) ? $_POST['email'] : '';
    $output = ['email' => $email];
    header("Content-Type: application/json");
    echo json_encode($output);
    // $post_data['u'] and $post_data['id'] are required hidden field per:
    // http://kb.mailchimp.com/lists/signup-forms/host-your-own-signup-forms
    $post_data['u'] = '150ec2a8a7363d28b01c6abd9';
    $post_data['id'] = 'a11ba1e49c';
    // $post_data['MERGE0'] represents the value of my email submission input tag's name attribute.
    // In my case the attribut of name="MERGE0", so $post_data['MERGE0'] is used as a variable.
    $post_data['MERGE0'] = urlencode($_POST['email']);
    foreach($post_data as $key => $value) {
        $post_items[] = $key.
        '='.$value;
    }
    $post_string = implode('&', $post_items);
    // Replace URL with your own. In the case of MailChimp, see:
    // http://kb.mailchimp.com/lists/signup-forms/host-your-own-signup-forms
    $curl_connection = curl_init('https://searchwilderness.us6.list-manage.com/subscribe/post');
    curl_setopt($curl_connection, CURLOPT_CONNECTTIMEOUT, 30);
    curl_setopt($curl_connection, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl_connection, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($curl_connection, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($curl_connection, CURLOPT_POSTFIELDS, $post_string);
    curl_exec($curl_connection);
    curl_close($curl_connection);
}
?>