During iPhone update to iOS 10.3.1, I was asked for my password using the correct machine name for my Mac mini. To be clear, the request was not for my iCloud password, my actual local user account password for macOS. This can also happen in the other direction – setting up a Mac may ask for verification for you to enter your iPhone / iPad passcode (and not your iCloud password)
I could not find any information about this kind of access. I was thinking it was security for iCloud and possibly related to two step authorization or two factor authorization. This is the first time I can think of that I entered a desktop password outside of that actual desktop.
I don't have a screen shot but I recall an implication that some files in my Mac are encrypted and need my password. '… need to enter the password for .'
Are there settings I can I control this assuming it's a legitimate part of iCloud setup process or iOS setup process?
Best Answer
When you reset all settings or restore a backup from iCloud (or set up a device as new), the Keychain / iCloud and local USB trust pairings are removed and you should be prompted to trust the Mac when it connects to your iPhone.
After the trust setting dialog pops up (if you are connected over USB), there is now a screen that asks you to enter your iCloud password to finish setting up the iOS device. I have not seen the follow on passcode/password page ever until today. In my case, it wanted the passcode on another iPad and not a Mac ( I have two iPads, an iPhone, Apple Watch, two Mac connected to my iCloud account as primary accounts / keychain sync enabled on all).
Enter Passcode for Other iPad
In my case, the iPad in question is named iPad Air 2 and there's a blue link with the text "Forgot iPad Air 2 passcode?" Tapping that lets me select another device to enter a passcode. I then selected my Mac Pro and the text changes to:
Enter Mac Pro Password
I do have two step authentication enabled for my iCloud account so this seems a legitimate change that Apple has implemented recently to secure backups and/or joining a "new" device or OS to the keychain syncing / trust chain.
After entering the password, there was a long delay (the iPad screen went dark) and the next step was the iCloud Keychain dialog which also was slow to continue when I tapped that.