Store Necessary Data For Notifications

[adrastaea]

Summary

Determine the minimal set of information needed to decrypt and display messages in push notifications, and store them in app groups and keychains as appropriate.

Background

In order to decrypt messages for display, we will probably need to know:

1. Latest generation of member key
2. communityId's of communities they are a member of
3. userId's for users they are in those communities

Acceptance Criteria

• App Group created in Apple Developer Portal
• App Group added to NSE target entitlements
• Keychain Access Group configured
• Keychain Access Group added to both targets' entitlements
• Helper class created for shared UserData access
• Helper class created for shared Keychain access
• Pass data to native app on rn_bridge when keys rotate or communities are joined

[holmesworcester]

We probably want to store a few generations of member keys and we'll want more keys as we store more for DMs or private channels. Storing or having access to (via App Group) all the keys from the sigchain doesn't seem so unreasonable since it should be an O(1) lookup on a list of keys.

[holmesworcester]

Let's push on this for ways we can simplify it.