Oauth2Client and Microsoft Graph client_credentials

Hey,

I've now resorted into using a workaround, but here is something that would be nice to get working properly using oauth2_client. I was trying to create Oauth2Client plugin for Microsoft Graph client_credentials grant type but something is not right. Here is couple of code samples to illustrate my problem.

Here is reference code, from https://docs.microsoft.com/en-us/graph/sdks/create-client?tabs=PHP

// PHP client currently doesn't have an authentication provider. You will need to handle
// getting an access token. The following example demonstrates the client credential
// OAuth flow and assumes that an administrator has consented to the application.
$guzzle = new \GuzzleHttp\Client();
$url = 'https://login.microsoftonline.com/' . $tenantId . '/oauth2/token?api-version=1.0';
$token = json_decode($guzzle->post($url, [
    'form_params' => [
        'client_id' => $clientId,
        'client_secret' => $clientSecret,
        'resource' => 'https://graph.microsoft.com/',
        'grant_type' => 'client_credentials',
    ],
])->getBody()->getContents());
$accessToken = $token->access_token;

and that reference code is working for me in my tests.

If I try to get that $accessToken string with Oauth2Client plugin, like

$token = \Drupal::service('oauth2_client.service')->getAccessToken('MY_PLUGIN');
$accessToken = $token->getToken();

I do get a string token out from that, but it is not working one.

If I take all parameters from MY_PLUGIN and use it with the reference code, like

$guzzle = new \GuzzleHttp\Client();
$o365 = \Drupal::service('oauth2_client.service')->getClient('MY_PLUGIN');
$token = json_decode($guzzle->post($o365->getTokenUri(), [
  'form_params' => [
    'client_id' => $o365->getClientId(),
    'client_secret' => $o365->getClientSecret(),
    'resource' => $o365->getAuthorizationUri(),
    'grant_type' => $o365->getGrantType(),
  ],
])->getBody()->getContents());
$accessToken = $token->access_token;

I once again have a working token.

Any ideas what I may be missing?