iOS: Stop covering the UI with the boot splash when the app only goes inactive - #106097

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Codex Review Summary

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@daledah Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

@Expensify/design Hey, I wanted to ask for your opinion on this change.

Context:
After the security audit, the app on iOS shows the splash screen as soon as it loses focus, so the app switcher snapshot never contains sensitive data. This also made it show up when opening Control Center or Notification Center. With this PR the splash screen covers the app only once it actually goes to the background, the same way e.g. Revolut does it (they show their passcode screen instead of a splash). The saved snapshot still shows only the splash, so the audit finding stays covered. We discussed it here on Slack.

What do you think? Does this feel like a good improvement?

I'm honestly not sure—most of my banking apps follow the same pattern we current have (splash even under control center). What are the security implications of the option you've prepared? Does it undo any of the security we baked into the current pattern? I think if we're good from a security perspective, I'm down with it. But otherwise, I'd like to get broader team buy-in since I assume we added that backgrounding for a good reason.

@dannymcclain Both options satisfy the Group-IB audit finding. The finding was about the app-switcher snapshots that the mobile devices save to disk and with either option those snapshots only ever contain the splash. So nothing we added for the audit gets undone. The only difference is UX.

The "before" option is the one that got reported as a regression (for an unexpected splash over Control Center). When we discussed it on Slack, the "after" option was deemed to feel smoother and less in the way (fair point imo). I do get that covering the screen more aggressively can make the app feel more secure too.

I don't think I have a strong opinion. I agree that the After screenshot feels a little less jarring, so as long as it still satisfies security requirements, I am down with it.

For some reason though, the bottom tabs in your screenshot do not feel correct - you might need a fresh pull of main?

I agree that the After screenshot feels a little less jarring, so as long as it still satisfies security requirements, I am down with it.

I feel the same. If we're still meeting whatever security requirements we need to, I'm down with that version.

For some reason though, the bottom tabs in your screenshot do not feel correct - you might need a fresh pull of main?

Yup, good catch! It's not from this PR, so it should go away with a fresh main

@daledah It looks like we're aligned on the "after" version, so you can go ahead with the review

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Screenshots/Videos

I feel the same. If we're still meeting whatever security requirements we need to, I'm down with that version.

This is exactly where I am too. I've noticed Wise does this too. I think it's mostly a security question. I don't mind whats there or the after.

Given we did this initially do we need to check with someone to ensure that we're not breaking a security requirement we need?

Here's the full report for clarity:

Vulnerability: Exposure of Sensitive Data in Screenshots
Platform: Android/ iOS
Risk: Medium
Description: Sensitive information may be disclosed through application screenshots created by the operating system when the application is moved to the background.
Recommendation: On Android, set the FLAG_SECURE window flag to prevent the OS from capturing application screenshots. On iOS, implement applicationDidEnterBackground and applicationDidBecomeActive to hide and restore sensitive data when the application transitions between foreground and background states (e.g., apply a blur effect while backgrounded)

So for me this checks all boxes.

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