What purpose do shared web credentials in a Message Filter Extension serve?

I'm experiencing the same situation as this post from several months ago, which never received an answer to their follow up question. https://forums.developer.apple.com/forums/thread/759255

The documentation for adding a message filter extension says "you must set up shared credentials as described in Shared Web Credentials"

(https://developer.apple.com/documentation/sms_and_call_reporting/sms_and_mms_message_filtering/creating_a_message_filter_app_extension)

However credentials are not forwarded to the server and calling SecAddSharedWebCredential from within the extension isn't possible.

So I don't understand why the documentation states Shared Web Credentials must be set up. After setting them up, then what is expected to happen with them, or what are you supposed to do with them next. The documentation just says to set them up, it doesn't say how/if they are used or how to use them in the specific context of a message filter extension