Persist GroupKeys

[timoxley]

Stores keys in system config directory on server or localstorage in browser (stubbed in, yet to be tested).

Needs

• Hook up webpack module replacement and test browser implementation.
• Explicit tests for loading keys, currently just ensures existing tests pass.
• Tests around concurrent access to config, ensure clobbering isn't possible.

Maybe

• Audit tests to ensure they clean up persisted data.
• Optimise storage format (doesn't need to store both hex string & Buffer string).
• Encryption/Decryption using client's keys.
• Instructions on how to take backups, specifically for publishers.
• Configurable storage location?
• Benchmarking, system is currently fully sync so may be problematic.

[linear]

NET-156 Persist encryption keys in JS client

The JS client currently includes an in-memory store for encryption keys. We should add an option for persistent storage, so that keys aren't lost across process restarts / page reloads.

A simple persistent key-value store is basically be enough. Sure, it's not very secure to store the keys in plaintext, but it's good enough as a first step at least.

But how to persist keys in a way that works in both node.js as well as browser, ideally without platform-specific code in the client library? Is there a drop-in replacement for localStorage for node.js? Maybe this?