Webhook OAuth - How do I exchange a webhook authorization code for an access token?

Question

I'm trying to use the oauth approach of adding webhooks to channels within Discord. The workflow is that a user authenticates with my application using OAuth. Then I redirect them to:

ApiClient::API_URL.'/oauth2/authorize?client_id='.Discord::appKey().'&scope=webhook.incoming&redirect_uri='.urlencode($webhookCallback->callbackUrl()).'&response_type=code');

The redirect URL works because it does allow the OAuth'd user to choose a server/channel.

When you exchange the authorization code for an access token, the token response will contain the webhook object:

I'm using the following request to try to convert the authorization code into an access token with no luck:

    $client = new Client();
    $response = $client->post('https://discordapp.com/api/oauth2/token', [
        'headers' => [
            'Accept' => 'application/json'
        ],
        'form_params' => [
            'grant_type' => 'authorization_code',
            'client_id' => env('DISCORD_APP_KEY'),
            'client_secret' => env('DISCORD_APP_SECRET'),
            'redirect_uri' => url('/discord/webhook-authorized'),
            'code' => $request->get('code')
        ],
    ]);

The response I get from the API is:

Client error: `POST https://discordapp.com/api/oauth2/token` resulted in a `401 UNAUTHORIZED` response:
{"error": "access_denied"}

What grant type do I need to complete this request?

Answer 1

'grant_type' => 'authorization_code',

needed to be

'grant_type' => 'client_credentials',