fix(federation): handshake sourceOrigin honors PUBLIC_ORIGIN (align with S2S auth origin)

packages/server/src/routes/federation.peerInitiateOutbound.test.ts

@@ -41,11 +41,16 @@ vi.mock('../utils/auth.js', () => ({
   requireAdmin: async () => {},
 }));
 
+// getOurOrigin returns an origin DISTINCT from `https://${config.domain}`
+// (config.domain === 'local.example'). This simulates PUBLIC_ORIGIN being set
+// to something other than https://DOMAIN — the exact configuration that exposed
+// the handshake/S2S-auth origin desync (BUG: resolveLocalOrigin used DOMAIN).
+const PUBLIC_ORIGIN = 'https://public.example';
 vi.mock('../utils/federationAuth.js', async () => {
   const actual = await vi.importActual<typeof import('../utils/federationAuth.js')>('../utils/federationAuth.js');
   return {
     ...actual,
-    getOurOrigin: () => 'https://local.example',
+    getOurOrigin: () => 'https://public.example',
     generateHmacSecret: () => 'mock-generated-secret',
   };
 });
@@ -134,6 +139,39 @@ describe('POST /api/federation/peer/initiate — 202 token capture & 200 clear',
     expect(peer?.approvalToken).toBe(remoteToken);
   });
 
+  it('handshake sourceOrigin equals getOurOrigin() (honors PUBLIC_ORIGIN), not https://DOMAIN', async () => {
+    const fetchSpy = vi.spyOn(globalThis, 'fetch').mockResolvedValue(
+      new Response(
+        JSON.stringify({ accepted: true, instanceName: 'Remote' }),
+        { status: 200, headers: { 'Content-Type': 'application/json' } },
+      ),
+    );
+
+    const response = await app.inject({
+      method: 'POST',
+      url: '/api/federation/peer/initiate',
+      payload: { remoteOrigin: 'https://remote.example' },
+    });
+
+    expect(response.statusCode).toBe(200);
+
+    // Locate the outbound handshake call to the remote /peer/accept endpoint.
+    const acceptCall = fetchSpy.mock.calls.find(([url]) =>
+      String(url) === 'https://remote.example/api/federation/peer/accept',
+    );
+    expect(acceptCall).toBeDefined();
+
+    const init = acceptCall![1] as RequestInit;
+    const body = JSON.parse(String(init.body)) as { sourceOrigin: string };
+
+    // The handshake sourceOrigin MUST match the origin used for S2S auth
+    // (getOurOrigin / PUBLIC_ORIGIN), so the responder keys the peer row by the
+    // same value it will later see in X-Federation-Origin.
+    expect(body.sourceOrigin).toBe(PUBLIC_ORIGIN);
+    // And it must NOT fall back to https://DOMAIN when PUBLIC_ORIGIN differs.
+    expect(body.sourceOrigin).not.toBe('https://local.example');
+  });
+
   it('on 200 from remote, activates and clears approvalToken', async () => {
     vi.spyOn(globalThis, 'fetch').mockResolvedValue(
       new Response(

packages/server/src/routes/federation.ts

@@ -62,20 +62,17 @@ function sanitizePeer(row: typeof schema.federationPeers.$inferSelect): Sanitize
 }
 
 /**
- * Determine this instance's public origin.
- * Prefer the explicit DOMAIN env var; fall back to the request Host header.
+ * Determine this instance's public origin for the peering handshake.
+ *
+ * Delegates to `getOurOrigin()` so the handshake `sourceOrigin` is IDENTICAL to
+ * the `X-Federation-Origin` value used for authenticated S2S requests. This
+ * honors `PUBLIC_ORIGIN` (getOurOrigin's precedence: PUBLIC_ORIGIN →
+ * `https://${DOMAIN}` → `http://localhost:${PORT}`). Using DOMAIN directly here
+ * previously desynced the responder's peer-row key from the auth origin,
+ * causing permanent `403 Not peered` whenever PUBLIC_ORIGIN != https://DOMAIN.
  */
-function resolveLocalOrigin(request: { headers: Record<string, string | string[] | undefined> }): string {
-  if (config.domain) {
-    return `https://${config.domain}`;
-  }
-  const hostHeader = request.headers.host;
-  const host = Array.isArray(hostHeader) ? hostHeader[0] : hostHeader;
-  if (!host) {
-    throw new Error('Cannot determine local origin: no DOMAIN configured and no Host header');
-  }
-  const protocol = (request as Record<string, unknown>).protocol === 'https' ? 'https' : 'http';
-  return `${protocol}://${host}`;
+function resolveLocalOrigin(): string {
+  return getOurOrigin();
 }
 
 /**
@@ -861,7 +858,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
 
       let localOrigin: string;
       try {
-        localOrigin = resolveLocalOrigin(request);
+        localOrigin = resolveLocalOrigin();
       } catch {
         return reply.code(500).send({
           error: 'Cannot determine local instance origin. Set the DOMAIN environment variable.',
@@ -1883,7 +1880,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
 
       let localOrigin: string;
       try {
-        localOrigin = resolveLocalOrigin(request);
+        localOrigin = resolveLocalOrigin();
       } catch {
         return reply.code(500).send({
           error: 'Cannot determine local instance origin. Set the DOMAIN environment variable.',
@@ -2138,7 +2135,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
       const newSecret = generateHmacSecret();
       let localOrigin: string;
       try {
-        localOrigin = resolveLocalOrigin(request);
+        localOrigin = resolveLocalOrigin();
       } catch {
         return reply.code(500).send({
           error: 'Cannot determine local instance origin. Set the DOMAIN environment variable.',
@@ -3073,7 +3070,7 @@ export async function federationRoutes(app: FastifyInstance): Promise<void> {
 
         let localOrigin: string;
         try {
-          localOrigin = resolveLocalOrigin(request);
+          localOrigin = resolveLocalOrigin();
         } catch {
           localOrigin = config.domain ? `https://${config.domain}` : '';
         }