Allow setting a allowList for rooms

- prevents from joining & showing not allowed rooms if enabled
- prevents from listing such rooms in room directory as well (with bad UX for now)

config/config.default.json

@@ -21,4 +21,9 @@
 
   // Secrets
   //"matrixAccessToken": "xxx"
+
+  // Restrict to rooms listed below
+  //"enableAllowList": true,
+  // use room ids starting with a `!`, not aliases
+  //"roomAllowList": ["!ypQyNeReyEPUCKYjPU:matrix.org"],  // e.g. room about Matrix Reputation
 }

server/lib/matrix-utils/check-room-allowed.js

@@ -0,0 +1,27 @@
+'use strict';
+
+const assert = require('assert');
+
+const fetchRoomId = require('./fetch-room-id');
+
+const config = require('../config');
+const basePath = config.get('basePath');
+assert(basePath);
+const matrixServerUrl = config.get('matrixServerUrl');
+assert(matrixServerUrl);
+
+config.defaults({
+  "enableAllowList": false,
+  "roomAllowList": [],
+});
+
+async function checkIfAllowed(roomIdOrAlias) {
+  if (!config.get("enableAllowList")) {
+    return true;
+  }
+  const roomId = await fetchRoomId(roomIdOrAlias);
+  const result = config.get("roomAllowList").includes(roomId)
+  return result;
+}
+
+module.exports = checkIfAllowed;

server/lib/matrix-utils/ensure-room-joined.js

@@ -5,6 +5,7 @@ const urlJoin = require('url-join');
 
 const StatusError = require('../errors/status-error');
 const { fetchEndpointAsJson } = require('../fetch-endpoint');
+const checkIfAllowed = require('./check-room-allowed');
 const getServerNameFromMatrixRoomIdOrAlias = require('./get-server-name-from-matrix-room-id-or-alias');
 const MatrixViewerURLCreator = require('matrix-viewer-shared/lib/url-creator');
 
@@ -21,6 +22,11 @@ async function ensureRoomJoined(
   roomIdOrAlias,
   { viaServers = new Set(), abortSignal } = {}
 ) {
+  const result = await checkIfAllowed(roomIdOrAlias);
+  if (!result) {
+    throw new StatusError(403, `Bot is not allowed to view room, room is not listed in explicit allow list.`);
+  }
+
   // We use a `Set` to ensure that we don't have duplicate servers in the list
   assert(viaServers instanceof Set);
 

server/lib/matrix-utils/fetch-room-id.js

@@ -0,0 +1,45 @@
+'use strict';
+
+const assert = require('assert');
+const urlJoin = require('url-join');
+
+const StatusError = require('../errors/status-error');
+const { fetchEndpointAsJson } = require('../fetch-endpoint');
+
+const config = require('../config');
+const basePath = config.get('basePath');
+assert(basePath);
+const matrixServerUrl = config.get('matrixServerUrl');
+assert(matrixServerUrl);
+
+config.defaults({
+  "enableAllowlist": false,
+  "roomAllowlist": [],
+});
+
+async function fetchRoomId(
+  roomIdOrAlias,
+) {
+  if (roomIdOrAlias.startsWith("!")) {
+    return roomIdOrAlias;
+  }
+
+  const resolveEndpoint = urlJoin(
+    matrixServerUrl,
+    `_matrix/client/v3/directory/room/${encodeURIComponent(roomIdOrAlias)}`
+  );
+  try {
+    const { data: roomData } = await fetchEndpointAsJson(resolveEndpoint, {
+      method: 'GET',
+    });
+    assert(
+      roomData.room_id,
+      `Alias resolve endpoint (${resolveEndpoint}) did not return \`room_id\` as expected. This is probably a problem with that homeserver.`
+    );
+    return roomData.room_id;
+  } catch (err) {
+    throw new StatusError(403, `Bot is unable to resolve alias of room: ${err.message}`);
+  }
+}
+
+module.exports = fetchRoomId;

server/routes/room-directory-routes.js

@@ -10,6 +10,7 @@ const { DIRECTION } = require('matrix-viewer-shared/lib/reference-values');
 const RouteTimeoutAbortError = require('../lib/errors/route-timeout-abort-error');
 const UserClosedConnectionAbortError = require('../lib/errors/user-closed-connection-abort-error');
 const identifyRoute = require('../middleware/identify-route-middleware');
+const checkIfAllowed = require('../lib/matrix-utils/check-room-allowed');
 const fetchAccessibleRooms = require('../lib/matrix-utils/fetch-accessible-rooms');
 const renderHydrogenVmRenderScriptToPageHtml = require('../hydrogen-render/render-hydrogen-vm-render-script-to-page-html');
 const setHeadersToPreloadAssets = require('../lib/set-headers-to-preload-assets');
@@ -81,6 +82,13 @@ router.get(
       }
     }
 
+    // limit to allow list
+    // Because filtering happens after checking the directory this may lead into a bad UX.
+    if (config.get("enableAllowList")) {
+      const checkResults = await Promise.all(rooms.map((r) => r.room_id).map(checkIfAllowed));
+      rooms = rooms.filter((_v, index) => checkResults[index]);
+    }
+
     // We index the room directory unless the config says we shouldn't index anything
     const stopSearchEngineIndexingFromConfig = config.get('stopSearchEngineIndexing');
     const shouldIndex = !stopSearchEngineIndexingFromConfig;