Fix initialization of authenticator

[itsmeichigo]

Closes WOOMOB-902

Description

We got crash reports in the LoginViewController.showLoginEpilogue step of the login flow. This method can fail in two cases:

• When the navigationController of the view controller cannot be found.
• When the authenticationDelegate is nil.

This PR mitigates the issue with some enhancements:

• Updates the initialization of the authenticator to allow initializing only once upon app start. Reasons behind this fix:
  • It's not necessary to initialize more than once.
  • The previous implementation allows the private instance to be recreated, breaking the delegate reference.
• Add messages to the fatalError in the login flow to better understand the issue if the above doesn't fix the crash.

Note: I'm targeting 23.0 for this PR as the crash is likely an edge case. Let me know if you think we should target the beta build 22.9 instead.

Testing steps

Test login using different scenarios:

• Log out of the app and try logging back in => confirm that login succeeds.
• Test login with magic link when the app is forced closed (detailed steps here).
• Test that connecting to existing site flow still works (detailed steps here)

Testing information

Tested the above test cases using simulator iPhone 16 iOS 18.4.

Screenshots

No UI changes.

---

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[wpmobilebot]

📲 You can test the changes from this Pull Request in WooCommerce iOS Prototype by scanning the QR code below to install the corresponding build.

	App Name	WooCommerce iOS Prototype
	Build Number	pr15953-df0a0df
	Version	22.9
	Bundle ID	com.automattic.alpha.woocommerce
	Commit	df0a0df
	Installation URL	2m12qvrelr2o8

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[RafaelKayumov]

LGTM, pre-approving. Left a couple of comments.

[RafaelKayumov]

Looks like the dotcomAuthScheme argument of initializeWithCustomConfigs method is no longer being passed and the ApiCredentials.dotcomAuthScheme default value is always used there. May be it's worth removing the method argument at all?

[itsmeichigo]

Removed in 40282f6.

[RafaelKayumov]

There is another configureAuthenticator call on line 292. Should it removed as well?

[itsmeichigo]

Thanks for catching this! Removed in b4f38e6.