This is fundamentally similar to how UPS, DHL etc. document how to recognise their tracking numbers.

"Their" and genitive in general doesn't necessarily mean ownership. It's often used for various sorts of connection. For example, "my address" doesn't claim ownership of either the street or the house, "my age", "my wife", all connected to me somehow but not owned by me.

They already did. That's what public means. This is just an optimization to make it harder for WeChat access tokens to be inadvertently compromised without getting noticed.

If you're worried about the Chinese government having inappropriate influence over or access to various things outside China, that's in general a valid concern indeed, but facilitating credential scanning in public repositories really doesn't seem worrying.