Login/logut methods in ios about apphudsdk

[vlr-code]

Hi @fury21
By default, Apphud SDK creates own unique UUID user identifiers for each device. On iOS, User ID is saved to keychain and persists after app reinstall, however on Android User ID is reset after each reinstall due to technical limitations. If you want Apphud to manage User ID for you (recommended), then just initialize SDK without passing any User ID. Apphud guarantees User ID uniqueness for each device.
You can also initialise SDK with custom Device ID. This should be used if you plan to use logout / login features. You are responsible for User ID uniqueness and User Merging in this case. Best practice is to pass the same identifier to Device ID and User ID.
You can update your user's ID at any time after SDK initialization. This can be useful if you get your User ID some time after launch -> Apphud.updateUserID
Log out method will clear all saved data and reset SDK to uninitialised state. You must initialize SDK again after this method call. Use this method if you have your own login-logout logic.

User Merging
By default, users are being merged only if their App Store Receipts match. For example, if Apphud has a customer A with App Store Receipt A and we receive a new request from customer B with App Store Receipt A, then both customers are merged into customer A and User ID of the latter one is changed to A.
In other words, Apphud merges users by their original transaction id.
The device ID is the main identifier that uniquely identifies a customer. So even if you initialize SDK with the same custom User ID on different devices, several new users with the same User ID will be created since they have different Device IDs.