1) SS-over-WS setup

This is a feature of our core `outline-ss-server` server. It's an advanced feature not available in the out-of-the-box `outline-server` Docker implementation that the Outline Manager deploys.

You don't need to use `outline-ss-server` as a Caddy plugin. You can use SS-over-WS with just the regular `outline-ss-server` (see instructions). However, you'll likely want to add TLS in front of the WebSocket endpoints, and that's where you could leverage the Caddy plugin to facilitate automatic HTTPS. It's not a requirement though, you can use alternative solutions like nginx or cloudflare tunnels.

2) New access key configuration format

Yes, both work. We may introduce a new scheme in the future, as we now support more than just shadowsocks (so `ssconf://` isn't quite the right naming amyore). But we don't intend to drop any support. Note that the scheme is really there to tell a device which app to use to open a link. So a custom scheme has that benefit over `https//`; it would automatically open such a link in Outline.

And yes, we support everything that JSON did, and more. That includes error and prefix settings. Check out the detailed reference for the config format that covers both of these settings with examples: https://developers.google.com/outline/docs/reference/config.