Parse Server affected by empty authData bypassing credential requirement on signup

Parse Server is an open source backend that can be deployed to any infrastructure that can run Node.js. Prior to 9.6.0-alpha.29 and 8.6.49, a user can sign up without providing credentials by sending an empty authData object, bypassing the username and password requirement. This allows the creation of authenticated sessions without proper credentials, even when anonymous users are disabled. The fix in 9.6.0-alpha.29 and 8.6.49 ensures that empty or non-actionable authData is treated the same as absent authData for the purpose of credential validation on new user creation. Username and password are now required when no valid auth provider data is present. As a workaround, use a Cloud Code beforeSave trigger on the _User class to reject signups where authData is empty and no username/password is provided.