invalid_client When Sending OAuth2 Request to Discord API - php

Question

So I've been working on a login system with Discord, and this is the first roadblock I've hit.
I'm trying to POST to /oauth2/token/revoke and it keeps giving me back the error "invalid_client".
I've tried using a client secret and not using it, only sending the token, changing the name "access_token" to "token", and a few other things I can't recall.
My code for sending the request is this:
session_start();
//debug thing
echo OAUTH2_CLIENT_ID;
$params = array(
"access_token" => $_SESSION["access_token"],
"client_id" => OAUTH2_CLIENT_ID
);
apiRequest("https://discordapp.com/api/oauth2/token/revoke", $params);
The code for that apiRequest function is adapted from a different thread on here and is as follows:
function apiRequest($url, $post=FALSE, $headers=array()) {
$ch = curl_init($url);
curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
$response = curl_exec($ch);
if($post) {
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($post));
$headers[] = 'Content-Type: application/x-www-form-urlencoded';
}
$headers[] = 'Accept: application/json, application/x-www-form-urlencoded';
if(isset($_SESSION["access_token"]))
$headers[] = 'Authorization: Bearer ' . $_SESSION["access_token"];
// using this to see my headers
var_dump($headers);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$response = curl_exec($ch);
$code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
if ($code != 200) {
//using this to see the error
echo $response;
exit();
fatalError($code, $_SERVER[REQUEST_URI]);
}
return $response;
}
And yes, both the access token and client ID are valid. They work properly on other requests and I've displayed them on this page and confirmed them to be valid.
Any ideas? Am I missing something stupid?

Answer 1

Worked out the fields you need and fiddled with curl a bit and this code is working.
$params = array(
"token" => $_SESSION["access_token"],
"client_id" => OAUTH2_CLIENT_ID,
"client_secret" => OAUTH2_CLIENT_SECRET
);
$ch = curl_init("https://discord.com/api/oauth2/token/revoke");
curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($params));
$headers[] = 'Content-Type: application/x-www-form-urlencoded';
$headers[] = 'Accept: application/json';
$headers[] = 'Authorization: Bearer ' . $_SESSION["access_token"];
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$response = curl_exec($ch);
$code = curl_getinfo($ch, CURLINFO_HTTP_CODE);
if ($code != 200) {
#error handling
}
curl_close($ch);