fix: gate cookie secure flag on TRUST_PROXY not NODE_ENV

secure:true cookies are only sent by browsers over HTTPS connections.
When NODE_ENV=production (always set in the Docker container) but no
TLS proxy is in front, the browser receives the cookie on login but
refuses to send it on subsequent HTTP requests — causing every
authenticated endpoint (/stream, /status, etc.) to return 401.

The correct signal is TRUST_PROXY: it is only set when a TLS-terminating
reverse proxy is confirmed to be in front. Affects emby_user and
csrf_token cookies across login, /csrf refresh, and logout.

server/routes/auth.js

@@ -70,13 +70,15 @@ router.post('/login', loginLimiter, async (req, res) => {
     // Set authentication cookie (signed when COOKIE_SECRET is set).
     // rememberMe=true  → persistent cookie, expires in 30 days
     // rememberMe=false → session cookie, expires when browser closes
-    // secure is always true — the app should sit behind HTTPS in production;
-    // behind a reverse proxy set TRUST_PROXY=1 so req.secure works correctly.
+    // secure:true only when TRUST_PROXY is set — i.e. a TLS-terminating reverse
+    // proxy is in front. Without it the app may be accessed over plain HTTP and
+    // secure cookies would never be sent back by the browser.
     const cookiePayload = JSON.stringify({ id: user.Id, name: user.Name, isAdmin });
     const signed = !!process.env.COOKIE_SECRET;
+    const secureCookie = !!process.env.TRUST_PROXY; // only send over HTTPS when behind a TLS proxy
     const cookieOptions = {
       httpOnly: true,
-      secure: process.env.NODE_ENV === 'production',
+      secure: secureCookie,
       sameSite: 'strict',
       signed,
       path: '/'
@@ -91,7 +93,7 @@ router.post('/login', loginLimiter, async (req, res) => {
     const csrfToken = crypto.randomBytes(32).toString('hex');
     res.cookie('csrf_token', csrfToken, {
       httpOnly: false, // intentionally readable by JS for the double-submit pattern
-      secure: process.env.NODE_ENV === 'production',
+      secure: secureCookie,
       sameSite: 'strict',
       path: '/'
     });
@@ -142,7 +144,7 @@ router.get('/csrf', (req, res) => {
   const csrfToken = crypto.randomBytes(32).toString('hex');
   res.cookie('csrf_token', csrfToken, {
     httpOnly: false,
-    secure: process.env.NODE_ENV === 'production',
+    secure: !!process.env.TRUST_PROXY,
     sameSite: 'strict',
     path: '/'
   });
@@ -168,14 +170,14 @@ router.post('/logout', async (req, res) => {
   }
   res.clearCookie('emby_user', {
     httpOnly: true,
-    secure: process.env.NODE_ENV === 'production',
+    secure: !!process.env.TRUST_PROXY,
     sameSite: 'strict',
     signed: !!process.env.COOKIE_SECRET,
     path: '/'
   });
   res.clearCookie('csrf_token', {
     httpOnly: false,
-    secure: process.env.NODE_ENV === 'production',
+    secure: !!process.env.TRUST_PROXY,
     sameSite: 'strict',
     path: '/'
   });