Adding an external tester group to existing build on testflight

[httran13]

Hello, this question is an extension of #13970.

I would like to add an existing external testing group to an existing build on testflight. The example from the above thread shows this can be done with

  app = Spaceship::Tunes::Application.find(CredentialsManager::AppfileConfig.try_fetch_value(:app_identifier))
  ...
  build = train.last
  group = Spaceship::TestFlight::Group.find(app_id: app.apple_id, group_name:"#{options[:group]}")
  build.add_group!(group)

but this requires you to use Spaceship::Tunes.login

I've search through the docs and code and looks liek theres also an Spaceship::ConnectAPI.auth method which uses API keys, which am able to get working and have tried passing the client with Spaceship::TestFlight::Base.set_client(client) without any success of getting Spaceship::Tunes to authenticate without a username and password.

Question is, is this even possible? as it seems Tunes is only restricted to .login() type

Thank you!