I need a official document about that.
Apple rarely publishes official documentation about what you can’t do; the documentation tends to focus on what you can do, and that’s certainly the case here.
Still, it’s true that iOS has no API for getting GPS timestamps.
Many developers have asked about getting tamper-resistant timestamps on iOS. The only guaranteed solution here is to use the network to get a timestamp from a server you trust. You can do other things but nothing that’s truly secure.
Regardless of how you proceed on current systems, I encourage you to file an enhancement request describing your requirements. While we may have seen similar requests many times before, a fresh bug report will allow you to express your needs in your own terms, and allow iOS engineering to gauge the level of demand.
Please post your bug number, just for the record.
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Quinn “The Eskimo!”
Apple Developer Relations, Developer Technical Support, Core OS/Hardware
let myEmail = "eskimo" + "1" + "@apple.com"