Can't get oauth2 to work

With versión 6 of simple_auth you also need https://www.drupal.org/project/simple_oauth_password_grant → , because password grant was removed and entity_share uses password to authenticate the users.

Thanks, I'll give that a try when we get around to that project again. If it works, it's probably worth a mention on the project page and/or readme of the entity share module.