gistfile1.txt

<?php

//Check to make sure the token is valid
if (!isset($_POST['token']) || $_POST['token'] != SLACK_TOKEN) {
  throw new Exception("Shenanigans!");
}

/*
 * This sends a message back to the user immediately so they know something's happening.
 * The `ignore_user_abort` allows the script to keep running,
 * even after the user has disconnected
 */
ignore_user_abort(true);
ob_start();
echo('{ "text": ":timer_clock: Doing some stuff, please wait..."}');
header($_SERVER["SERVER_PROTOCOL"] . " 200 OK");
header("Content-Type: application/json");
header('Content-Length: ' . ob_get_length());
ob_end_flush();
ob_flush();
flush();

//Wait for 5 seconds
sleep(5);

$payload = [
    'text' => 'Hello World!'
];

//Send the final response back to the webhook
$curl = curl_init();
curl_setopt_array($curl, array(
    CURLOPT_URL => $params['response_url'],
    CURLOPT_POST => true,
    CURLOPT_HTTPHEADER => array("Content-Type:  application/json"),
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POSTFIELDS => json_encode($payload)
));
$resp = curl_exec($curl);
curl_close($curl);