Bind Reddit and Matrix session identities

extensions/reddit-session-exporter/service-worker.js

@@ -1,4 +1,7 @@
-import { createSessionExportDownload } from './session-export.js';
+import {
+  assertMatchingSessionIdentity,
+  createSessionExportDownload,
+} from './session-export.js';
 
 const MATRIX_URLS = [
   'https://matrix.redditspace.com/*',
@@ -27,6 +30,29 @@ chrome.webRequest.onBeforeSendHeaders.addListener(
   ['requestHeaders', 'extraHeaders'],
 );
 
+chrome.cookies.onChanged.addListener(async ({ cookie }) => {
+  if (!['reddit_session', 'token_v2'].includes(cookie.name)) return;
+  await chrome.storage.local.remove('matrixCapture');
+  await chrome.action.setBadgeText({ text: '' });
+  await chrome.action.setTitle({
+    title: 'Reddit account changed. Open Reddit Chat before exporting.',
+  });
+});
+
+async function getRedditIdentity() {
+  const response = await fetch('https://www.reddit.com/api/me.json', {
+    credentials: 'include',
+    cache: 'no-store',
+  });
+  if (!response.ok) throw new Error('Reddit cookies did not authenticate. Sign in and try again.');
+  const payload = await response.json();
+  const account = payload?.data ?? payload;
+  if (!account?.name || !account?.id) {
+    throw new Error('Reddit did not return an authenticated account identity.');
+  }
+  return { username: account.name, accountId: account.id };
+}
+
 async function showError(message) {
   await chrome.action.setBadgeText({ text: 'ERR' });
   await chrome.action.setBadgeBackgroundColor({ color: '#dc3545' });
@@ -48,6 +74,14 @@ chrome.action.onClicked.addListener(async () => {
     const identity = await whoami.json();
     if (!identity?.user_id) throw new Error('Reddit Chat did not return an account identity.');
 
+    const redditIdentity = await getRedditIdentity();
+    try {
+      assertMatchingSessionIdentity(redditIdentity, identity.user_id);
+    } catch (error) {
+      await chrome.storage.local.remove('matrixCapture');
+      throw error;
+    }
+
     await chrome.downloads.download({
       ...createSessionExportDownload(cookies, { ...matrixCapture, userId: identity.user_id }),
       saveAs: true,