What you might be able to do is create an HTTP node with basic auth of your clientId and secret, then submit the “obtain token” request with your clientId and scopes. This will give you an access token you can use in subsequent requests.
However ideally we’ll get client credentials grant type supported by the inbuilt OAuth2 credential type, if you’d like to see that go ahead and vote on this issue here Add client_credentials grant type feature for oauth2