Simple PHP example of using the indieauth.com API

indieauth-client.php

<?php
session_start();

if(array_key_exists('token', $_GET)) {
  // Verify the token with indieauth.com
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL, 'https://indieauth.com/session?token=' . $_GET['token']);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
  $auth = json_decode(curl_exec($ch));
  // If we got a reply, store the domain in the session
  if($auth && $auth->me) {
    $_SESSION['user'] = preg_replace('|https?://|', '', $auth->me);
  }
  // Redirect back to this page
  header('Location: ' . $_SERVER['PHP_SELF']);
  die();
}

// If the user is not logged in, display a login link
if(!array_key_exists('user', $_SESSION)) {
  header('HTTP/1.1 403 Forbidden');
  echo "Not logged in.<br /><br />\n";
  ?>
<form action="http://indieauth.com/auth" method="get">
  <label>Web Address:</label>
  <input type="text" name="me" placeholder="yourdomain.com" />
  <p><button type="submit">Sign In</button></p>
  <input type="hidden" name="redirect_uri" value="<?= 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['PHP_SELF'] ?>" />
</form>
  <?php
  die();
}

// Now the user is logged in, and their domain is stored in $_SESSION['user']

echo '<p>Welcome, ' . $_SESSION['user'] . '</p>';