Reuse LocalAuthentication context

[eaceto]

Changes

Please describe both what is changing and why this is important. Include:

• Added an instance of LAContext to the Keychain class in order to reuse it.
• Expose the LAContext as a read property in order to reuse it outside of the Keychain (In Auth0's CredentialManager, for example)

References

Please include relevant links supporting this change such as a:

• fix issue: Local Authentication is not reused #73

Testing

Please describe how this can be tested by reviewers. Be specific about anything not tested and reasons why. If helpful, please include manual testing steps as well.

1. Create an instance of Keychain and configure it to use LocalAuthentication an access when the device is unlocked

keychain = A0SimpleKeychain()
keychain.useAccessControl = true
keychain.defaultAccessiblity = .whenUnlockedThisDeviceOnly
keychain.setTouchIDAuthenticationAllowableReuseDuration(5.0)

let r1 = keychain.setString("TEST 1A", forKey: "KEY 1", promptMessage: "P1")
let r2 = keychain.setString("TEST 2A", forKey: "KEY 2", promptMessage: "P2")       

let v1 = keychain.string(forKey: "KEY 1", promptMessage: "P1B")
let v2 = keychain.string(forKey: "KEY 2", promptMessage: "P2B")

2. Enable FaceID via declaration in Info.plist

<key>NSFaceIDUsageDescription</key>
<string>Access Keychain</string>

3. When running the code in (1) the Passcode / Touch ID / Face ID local authentication will be asked only once (will be reused). With the current code it's asked every time a keychain operation is performed.

[ ] This change adds unit test coverage (or why not)

It does not include Unit Test. The Test requires UI Interaction in order to see the behavior

[X] This change has been tested on the latest version of the platform/language or why not

Tested on iOS 13.2

Checklist

[X] I have read the Auth0 general contribution guidelines

[X] I have read the Auth0 Code of Conduct

[X] All existing and new tests complete without errors

[Widcket]

Hi @eaceto, apologies for the delay. LAContext is only available on iOS and macOS. This library supports tvOS and watchOS as well, that's why the CI build is failing. Can you please put the feature behind platform checks in order to maintain compatibility?

[eaceto]

Hello Rita, how are you? Thanks for replying, and sorry for not fixing that earlier. I was on holidays.

Let me add this checks now in order to fix the CI errors. Thanks!

[eaceto]

Hi @Widcket ! All tests passed, now. If you want to perform a detailed review on the Pull Request, please let me know.

[eaceto]

@Widcket all changes where made, and branch was rebased to current master (due to a PR about SPM)