Document local device storage client option

[QuintinWillison]

TBC whether it'll be called storage or perhaps localStorage.

See ably/ably-java#681 for reference implementation.

┆Issue is synchronized with this Jira Task by Unito

[uxduck]

Some context

A new field on ClientOptions, called localStorage was added to allow users to provide a custom implementation of how LocalDevice and DeviceDetails are stored on the device. The reason this was added was to enable users to implement encryption, so that sensitive data, for example deviceSecret, deviceIdentityToken and registrationToken are not left unencrypted in SharedPreferences on the device. There is no example of how to implement this custom implementation with encryption anywhere though. Take a look at SharedPreferenceStorage.java for the default, unencrypted implementation.

IMHO The issue and PR was badly documented, and it's not clear how to write this documentation without having read the Ably-Java code base. Also, I am not sure the status of this feature in other SDKs.

Also see ably/ably-java#593 for more information about what this is.

[sync-by-unito]

➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-2769