Face ID and Touch ID have made it much easier to lock down iPhone X and previous iPhones and iPads so we're the only ones who can access our data. Face ID also — finally! — gives me the ability to lock down iCloud Keychain items so that I have to authenticate in apps and on the web before it will autofill my passwords and credit card information. That way, if I hand a friend, colleague, or stranger-in-need my device to quickly make an emergency call or look up something critical on the web, I don't have to worry about them placing orders on my dime.
(Sadly, Touch ID is currently considered too slow and cumbersome to be forced for web logins but should provide the same protection for in-app logins.)
But there's more on my iPhone and iPad than just my Keychain. There are my emails and messages, photos and videos, calendar and contacts. Apple provided the ability to lock Notes over a year ago but, since then, hasn't extended the functionality to any additional apps. It makes it downright hard to be paranoid.
I'm hoping Apple can address even more of my concerns in the next iPhone and iPad software update, iOS 12.
On board for GuestBoard
Apple could add the option to require Face ID or Touch ID to launch every app. Settings could offer a Secure toggle that engages the authentication system for built-in apps the way password managers and banking apps already do for third-party apps. People and institutions highly vested in security would no doubt love that, but it would add both complexity and an excessive amount of overhead.
A Guest Mode would be a simpler, more elegant solution.
With iOS 8, Apple refactored its system manager, SpringBoard, into several smaller, more focused components. In addition to BackBoard, which was already spun off to handle background tasks, Apple added Frontboard for foreground tasks and PreBoard to handle the Lock screen under secure, encrypted conditions. By extending Preboard with a full-on GuestBoard, iOS could provide a more functional and yet still secure device lending experience.
Similar to how the Lock screen currently allows for emergency calls and even grants access to your Medical ID card without the need to access the Home screen, it would be great if there was a Guest Mode in iOS that could provide access to a secure instance of Phone.app so a lost child could call their parents or WKWebView so a desperate conference attendee could pull up their hotel location.
"Secure" being the key consideration. Lock screen is perpetually torn between security and convenience. You can enable features like Notification Center, message previews, Control Center, Siri, Passbook, and more, and each one provides convenience at the expense of security and privacy. They also expose Apple to potential Lock screen bypasses. Just like you can disable features from the Lock screen, disabling the Guest Mode would allow for individuals to better choose their own balance.
What's more, figuring out the parameters would be a challenge. How many phone calls could a guest place and for how long? How many web pages could they access and for how long? How do you provide emergency access while preventing excessive and unintended voice and data charges? It's always easier to request a feature than to model all the ramifications and implement it in the real world.
But solving hard problems in ways that seem simple and obvious is what Apple does best.
Be our Guest
You can currently create something like Guest Mode using Guided Access. You can lock your iPhone or iPad to Safari and have it stay that way until your passcode unlocks it. You can even use it to restrict an iPad to a game if you want to give it to a child while they wait at a doctor's office or airport.
Guided Access isn't quick to set up, though, and wouldn't be practical in an urgent situation. With Guest Mode, if enabled, you could just swipe, tap, and hand over your iPhone or iPad without having to worry about anyone accessing anything else that's on it — or simply running away with it unlocked.
You could be a good Samaritan without having to risk your privacy, security, or property.
This feature request has been filed with Apple as rdar://35535596.