chore(web): harden post-auth redirects and legacy URL rewrite

CHANGELOG.md

@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - Added `/api/avatar` to resolve user profile pictures. [#1159](https://github.com/sourcebot-dev/sourcebot/pull/1159)
+- Hardened post-auth redirects with an explicit same-origin `redirect` callback in the NextAuth config, and switched the legacy `/~/...` URL rewrite from a 308 to a 301. [#1161](https://github.com/sourcebot-dev/sourcebot/pull/1161)
 
 ### Fixed
 - Bumped `postcss` to `8.5.10`. [#1155](https://github.com/sourcebot-dev/sourcebot/pull/1155)

packages/web/src/auth.ts

@@ -220,6 +220,26 @@ export const { handlers, signIn, signOut, auth } = NextAuth({
         }
     },
     callbacks: {
+        // Restrict post-auth redirects (sign-in / sign-out, `callbackUrl`,
+        // `redirectTo`) to the same origin as the application. This mirrors
+        // Auth.js's documented default; we set it explicitly so the protection
+        // is visible in code and not dependent on upstream defaults.
+        // @see https://authjs.dev/reference/core#redirect
+        async redirect({ url, baseUrl }) {
+            if (url.startsWith("/")) {
+                return `${baseUrl}${url}`;
+            }
+
+            try {
+                if (new URL(url).origin === baseUrl) {
+                    return url;
+                }
+            } catch {
+                // Malformed URL — fall through to baseUrl.
+            }
+
+            return baseUrl;
+        },
         async jwt({ token, user: _user }) {
             const user = _user as User | undefined;
             // @note: `user` will be available on signUp or signIn triggers.

packages/web/src/proxy.ts

@@ -1,3 +1,4 @@
+import { StatusCodes } from 'http-status-codes';
 import { NextResponse } from 'next/server'
 import type { NextRequest } from 'next/server'
 
@@ -27,12 +28,12 @@ export async function proxy(request: NextRequest) {
 
     if (url.pathname.startsWith('/~/')) {
         url.pathname = url.pathname.replace(/^\/~/, '');
-        return NextResponse.redirect(url, 308);
+        return NextResponse.redirect(url, StatusCodes.MOVED_PERMANENTLY);
     }
 
     if (url.pathname === '/~') {
         url.pathname = '/';
-        return NextResponse.redirect(url, 308);
+        return NextResponse.redirect(url, StatusCodes.MOVED_PERMANENTLY);
     }
 
     return NextResponse.next();