Slack Events PHP Response - php

Question

I'm working on an integration between Slack and Filemaker utilizing PHP. I am successful in having the code create a record in Filemaker based on the json request, and also have no trouble returning the challenge key to Slack.
However, I'm having trouble passing the header response 200 OK to Slack, while passing the challenge back. It looks like it has to be one or the other.
I've tried to move the HTTP header to different areas in the code, but haven't had any success so far.
Here is the current code:
<?php
$data = json_decode(file_get_contents('php://input'), true);
if (!isset($data["challenge"])) {
$body = $_SERVER['HTTP_X_SLACK_RETRY_REASON'];
require_once ('Filemaker.php');
//$body = file_get_contents('php://input');
$fm = new Filemaker();
$fm->setProperty('database', '');
$fm->setProperty('username', '');
$fm->setProperty('password', '');
$command = $fm->newPerformScriptCommand('PHP_RESPONSE', 'script', $body);
$result = $command->execute();
}
else {
header("Content-Type: text/plain");
header('X-PHP-Response-Code: 200', true, 200);
echo $data["challenge"];
}
?>
The result I expect is for the code to return the challenge code for Slack, while also returning an HTTP header of 200 OK.
Currently I can see I am receiving an error of "http_error" from Slack, which is what leads me to believe the problem is that the header is not being passed back successfully.
Any ideas on what is wrong, or suggestions on the right direction to proceed would be greatly appreciated.

Answer 1

The problem was occurring because for events slack doesn't send "challenge" as a parameter when sending events. It looks like echoing "challenge" is only needed when initially setting the URL for the events API.
I enclosed the challenge echo in a if statement that would only trigger if the challenge variable was present. After doing so the 200 OK was successfully passed.
Here is the code I used that solved the problem for me:
$data = json_decode(file_get_contents('php://input'), true);
if (isset($data["challenge"])) {
$message = [
"challenge" => $data["challenge"]
];
header('Content-Type: application/json');
echo json_encode($message);
}

Answer 2

The documentation is actually a bit inconsistent on this topic. It claims you can respond the challenge in plan text, but the example shows it as x-www-form-urlencoded.
To be on the safe side try returning the challenge as JSON. That works perfectly for me. You also do not need to explicitly set the HTTP 200 code.
Example code:
$message = [
"challenge" => $data["challenge"]
];
header('content-type: application/json');
echo json_encode($message);