Hello,
when testing configuration, I’ve got error message from oauth2 server (custom, made with https://bshaffer.github.io/oauth2-server-php-docs/): “The request method must be POST when requesting an access token (http://tools.ietf.org/html/rfc6749#section-3.2)”. It looks like the request made by your plugins sends data using GET method instead of POST. Is there any way to change request method in your plugin?