feat: add multi-domain OAuth callback handling

Support multi-domain OAuth flow with core backend:
- Update login link to pass callback URL parameter
- Handle /github-callback responses in proxy (set cookie + redirect)
- Use dynamic callback URL based on current domain

Author: TooAngel

public/index.html

@@ -69,14 +69,21 @@
         <div class="login">
           <p>
             Login with
-            <a href="/api/login">
+            <a id="login-link" href="/api/login">
               <img
                 src="/images/GitHub-Mark-120px-plus.png"
                 alt="GitHub logo linked to login"
                 width="30"
             /></a>
           </p>
         </div>
+        <script>
+          // Set callback URL for multi-domain OAuth
+          const loginLink = document.getElementById('login-link');
+          const callbackUrl = window.location.origin + '/api/github-callback';
+          const redirectUrl = '/dashboard';
+          loginLink.href = `/api/login?callback=${encodeURIComponent(callbackUrl)}&redirect=${encodeURIComponent(redirectUrl)}`;
+        </script>
         <div class="logo">
           <a href="/">
             <img src="/images/logo_world_driven.svg" alt="World driven logo"

server/proxy.js

@@ -79,7 +79,11 @@ async function handleProxy(req, res, next) {
     });
 
     // Handle auth callback - set httpOnly cookie
-    if (req.url === '/auth/callback' && response.ok) {
+    // Supports both /auth/callback (API flow) and /github-callback (redirect flow)
+    if (
+      (req.url === '/auth/callback' || req.url.startsWith('/github-callback')) &&
+      response.ok
+    ) {
       const data = await response.json();
       if (data.sessionId) {
         res.cookie('sessionId', data.sessionId, {
@@ -90,6 +94,11 @@ async function handleProxy(req, res, next) {
         });
         delete data.sessionId;
       }
+      // For github-callback, redirect to the specified URL
+      if (req.url.startsWith('/github-callback') && data.redirect) {
+        res.redirect(data.redirect);
+        return;
+      }
       res.status(response.status).json(data);
       return;
     }