Switchboard/lib/PushTask.php

<?php
use BarnabyWalters\Mf2;

class PushTask {

  public static function verify_subscription($subscription_id) {

    $subscription = db\get_by_id('subscriptions', $subscription_id);
    if($subscription) {
      $feed = db\get_by_id('feeds', $subscription->feed_id);

      $url = parse_url($subscription->callback_url);

      // Choose the expiration for the subscription
      $lease_seconds = 86400*3;
      $exp_ts = time() + $lease_seconds;
      $exp_date = date('Y-m-d H:i:s', $exp_ts);

      $push_params = [
        'hub.mode' => 'subscribe',
        'hub.topic' => $feed->feed_url,
        'hub.challenge' => $subscription->challenge,
        'hub.lease_seconds' => $lease_seconds
      ];

      if($q=k($url, 'query')) {
        parse_str($q, $existing_params);
        $push_params = array_merge($push_params, $existing_params);
      }
      $url['query'] = http_build_query($push_params);

      $url = build_url($url);

      $response = request\get_url($url, true);

      if(request\response_is($response['status'], 2) && $response['body'] == $subscription->challenge) {
        // The subscriber replied with a 2xx status code and confirmed the challenge string.
        // The subscription is confirmed and active.
        $subscription->date_confirmed = db\now();
        $subscription->lease_seconds = $lease_seconds;
        $subscription->date_expires = $exp_date;
        db\set_updated($subscription);
        $subscription->active = 1;
        $subscription->save();

      } else {
        // The subscriber did not confirm the subscription, so reject it

      }

      print_r($response);

    }

  }

}