I feel like this one must be the reviewer being extremely dense. It's not the responsibility of the app author here to hand hold the reviewer in what this all means, but I would venture to guess that the reviewer could be convinced if the submitter wrote down every little detail explaining what a "client" is and then showing other examples of apps with the same functionality.
I hope they get it sorted out.
So they make an Appeal Board to please the politicians and potential regulators and turns out it is completely useless?
They just want all their Apps to use Sign In with Apple and further lock customers into their ecosystem.
What is going on with Apple?
Another Apple reviewer that doesn't fully understand their own guidelines and rules..