feature: the firewall lets the Router Manager in on the internal interface.

ADR.md

@@ -189,3 +189,29 @@ options at all. They are recognised by name as before: `psk`, and options with `
 
 Consequences: No secret reaches the web service's state file or any answer of the API. A client
 cannot tell whether a secret is set. A new secret option still needs a name that matches.
+
+## ADR-9: The Router Manager is a separate package with a small Python server
+
+Status: Accepted
+
+Context: The router needs a web application to manage it, which may run on the router or on
+another Linux system. The router's web service needs a token signed with `web.jwt_secret` for
+`/config` and `/users` and sends no CORS headers, so a browser cannot call it with the secret
+kept away from the page.
+
+Decision: `vpn-router-manager` is a Debian package of its own, built in the repository `linux-cloud-router-manager`. A React and
+MUI application in the style of manage-ui is built with Vite when the package is built and
+shipped as static files. A Python server, using the Ubuntu packages `python3-jwt` and `python3-requests`, serves them and
+passes every `/api/<path>` call to the router's `/<path>`, signing a short-lived token with the
+router's secret; it holds no logic of the router's own. It reads its settings from
+`/etc/vpn-router-manager/manager.json` at each request; on the router the settings not given
+come from `vpn-router.json`, and it listens on the internal address like the status web
+service, with the same discovery thread. `vpn-router-setup` opens the manager's port on the
+internal interface while the manager is installed, so the firewall stays in one place. The
+manager asks for no authentication yet.
+
+Consequences: The router needs no Node.js; the package needs only `python3` and packages of the Ubuntu archive. The secret never
+reaches the browser. The application checks the shape of every answer of the router. Anyone who
+reaches the manager's port manages the router, so on another system it listens on `127.0.0.1`
+unless told otherwise. The router's firewall depends on whether the manager is installed, and a
+changed manager port needs `vpn-router-setup` to run again.