Allow user to lock app with pin or password

[ghost]

In celebration of #PasswordDay I am creating this issue and as we think about tour and splash screen UI we should create a lock screen for the app and add functionality to allow user to set a pin or password to add an extra layer of security over their app install so if their device is stolen or used by someone Glucosio can be locked independently of the OS.

[emilianbold]

iOS does not provide per-app passwords and it does not seem useful to implement it ourselves.

If we start pushing data into Health.app then we have another app without a separate password providing open access.

Implementation-wise we could go with https://github.com/recruit-lifestyle/Smile-Lock but on iOS I would just not implement this feature.

[chwalters]

Some apps do require a password for additional privacy

[emilianbold]

Sure, I understand the idea. But when the same data is available in the Apple Health.app, you are not securing much. And Apple itself doesn't seem to see this data important enough to warrant a 2nd level of protection.

It's P3 so I'll leave it last and see if I can make a prototype with Smile-Lock.

[chwalters]

Perhaps HealthKit integration should be optional, since some people might prefer that their data is not shared, and may want additional privacy that a PIN or password could help provide

[emilianbold]

If people deny Glucosio access to HelthKit in the confirmation screen, the data is not shared. Then we could have better security with a secondary password.