gistfile1.php

<?php
// fetches the host-meta.json file for the given domain/identifier. $scheme
// is the scheme from user input, $domain is the domain, and $identifier is
// the normalized user input. Returns an associative array containing the
// data from host-meta.json or false.
function fetch_host_meta($curl, $scheme, $domain, $identifier) {
  $query = '?uri=' . urlencode($identifier);

  // first try SSL
  curl_setopt($curl, CURLOPT_URL,
    'https://' . $domain . '/.well-known/host-meta.json' . $query);
  $host_meta = curl_exec($curl);

  // don't fallback to HTTP if the user explicitly said HTTPS
  if (!$host_meta && $scheme != 'https') {
    curl_setopt($curl, CURLOPT_URL,
      'http://' . $domain . '/.well-known/host-meta.json' . $query);
    $host_meta = curl_exec($curl);
  }
  
  // make sure we got something
  if (!$host_meta) {
    return false;
  }
  
  $host_meta = json_decode($host_meta, true);
  if (!isset($host_meta['openid']['token_endpoint'])) {
    return false;
  } else {
    return $host_meta;
  }
}