I also can't find any description on this. And I also can't get X-Rate-Limit in response, which is told in https://developer.apple.com/documentation/appstoreconnectapi/identifying_rate_limits

Have you get any description about the rate limit for appleid.apple.com/auth/token? If you got some, please show me, thanks. I tried to get an X-Rate-Limit HTTP header, which is told in https://developer.apple.com/documentation/appstoreconnectapi/identifying_rate_limits. But my response's header don't have this.