How to get Client ID and Redirect URI when implementing Sign in with Apple on another platform?

Hi Apple,

I am attempting to get Sign in with Apple working in the Unity editor. I intend to use Unity's REST functions to facilitate this. I have found an article (linked below) that describes "Incorporating Sign in with Apple into Other Platforms". I need to either generate or find my program's client_id. The article says "client_id: (Required) The developer’s client identifier, as provided by WWDR.". I not understand what WWDR is or how I can use it to get my client_id, I would love your help on this.

https://developer.apple.com/documentation/signinwithapplejs/incorporating_sign_in_with_apple_into_other_platforms

There don't seem to be any community guides on how to function as another platform, but there are some on building a web app. To function as a web app all the guides say that I need to create a Service ID. To add Sign in with Apple functionality to that ID I need to give it a web domain that will use Sign in with Apple. I am trying to build a Unity app, so this mandatory field seems strange to me, I am not sure what I ought to put there.

Even if I got my client id from WWDR, I would need a valid redirect uri. The article does not state how to set one of these. The only place that I have found to do so is in creating a Service ID. But if a Service ID is needed, it would also contain a client id, removing the need to use a WWDR. This all has led to me being quite confused. Could you please give me some pointers here, either about how to get / use WWDR or what the web domain field on Service ID's is supposed to mean if my application is not a web app? It would be really appreciated.

Thanks.