fix(auth): strip internal port from OAuth redirects on BYOD domains (#728)

* fix(auth): strip internal port from OAuth redirects on BYOD domains

When BYOD custom domains proxy auth requests through the dashboard to
PRIVATE_SERVER_URL (e.g. http://cio-api-vymh:10000), Node's URL host setter
preserves the upstream port. Better Auth then redirects browsers to
https://customer.example:10000/... which fails.

- Add oauth-proxy-redirect helpers to clear backend ports explicitly
- Rewrite inbound auth request URLs and outbound oauth-proxy-callback Location headers
- Send hostname-only X-Forwarded-Host from dashboard proxy when port matches backend

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(auth): address Greptile review on oauth port stripping

- Only treat PRIVATE_SERVER_URL as an internal backend port
- Add test for rewriteAuthRequestUrl when forwarded host still has :10000

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

apps/api/src/app.ts

@@ -6,6 +6,12 @@ import { isPublicCorsPath, sessionCors } from '@api/middlewares/cors';
 import { randomBytes } from 'crypto';
 
 import { API_SERVER_URL } from '@api/constants';
+import {
+  resolveOAuthBrowserOrigin,
+  rewriteAuthRequestUrl,
+  rewriteOAuthProxyCallbackLocation,
+  shouldRewriteOAuthProxyCallbackLocation
+} from '@api/utils/oauth-proxy-redirect';
 import { Hono } from '@api/utils/hono';
 import { ErrorCodes } from '@api/utils/errors';
 import { accountRouter } from '@api/routes/account';
@@ -114,13 +120,16 @@ export const app = new Hono()
     let request = c.req.raw;
     const fwdHost = c.req.header('x-forwarded-host');
     const fwdProto = c.req.header('x-forwarded-proto');
+    const browserOrigin = resolveOAuthBrowserOrigin({
+      forwardedHost: fwdHost,
+      forwardedProto: fwdProto
+    });
+
     if (fwdHost) {
-      const url = new URL(request.url);
-      url.host = fwdHost;
-      if (fwdProto === 'https' || fwdProto === 'http') {
-        url.protocol = `${fwdProto}:`;
-      }
-      request = new Request(url, request);
+      request = rewriteAuthRequestUrl(request, {
+        forwardedHost: fwdHost,
+        forwardedProto: fwdProto
+      });
     }
 
     // Inbound: if the browser is hitting `/oauth-proxy-callback?token=…`
@@ -168,8 +177,9 @@ export const app = new Hono()
     // pushes the Location header past Render's response size ceiling and
     // the redirect silently never reaches the browser.
     if (response.status >= 300 && response.status < 400) {
-      const location = response.headers.get('location');
-      if (location && location.includes('/oauth-proxy-callback') && location.includes('cookies=')) {
+      let location = response.headers.get('location');
+
+      if (location?.includes('/oauth-proxy-callback') && location.includes('cookies=')) {
         try {
           const outUrl = new URL(location);
           const cookies = outUrl.searchParams.get('cookies');
@@ -178,14 +188,22 @@ export const app = new Hono()
             await storeHandoffPayload(token, cookies);
             outUrl.searchParams.delete('cookies');
             outUrl.searchParams.set('token', token);
-            const headers = new Headers(response.headers);
-            headers.set('location', outUrl.toString());
-            return new Response(response.body, { status: response.status, headers });
+            location = outUrl.toString();
           }
         } catch (error) {
           console.error('[auth-handler] failed to swap cookies → token, falling back to inline cookies:', error);
         }
       }
+
+      if (location && browserOrigin && shouldRewriteOAuthProxyCallbackLocation(location, browserOrigin)) {
+        location = rewriteOAuthProxyCallbackLocation(location, browserOrigin);
+      }
+
+      if (location && location !== response.headers.get('location')) {
+        const headers = new Headers(response.headers);
+        headers.set('location', location);
+        return new Response(response.body, { status: response.status, headers });
+      }
     }
 
     if (response.status >= 300 && response.status < 400) {