fix: advertise the audience scope so tokens actually carry aud

The OAuth path to /api/mcp has never worked end to end. Every access token
arrived without an `aud` claim and jwt.ts rejected it with
"claim invalid: aud" (401), even though the handshake, consent and PKCE all
succeeded. Only the CLI HMAC path worked, because cli-token.ts sets the
audience itself — which is why this went unnoticed.

Cause: Authentik evaluates a scope mapping only when the client REQUESTS
that scope by name. An MCP client learns which scopes to request from
`scopes_supported` in our RFC 9728 protected-resource metadata, and we only
advertised openid/profile/email. So the `aud-shared-memory` mapping was
attached to the provider but never evaluated.

Advertise the audience scope in that metadata. Name is derived as
`aud-<OIDC_AUDIENCE>` to match the README convention, overridable with the
new optional OIDC_AUDIENCE_SCOPE for deployments that named it differently.

Also documents that Claude Code's RFC 8707 `resource` parameter is ignored
by Authentik 2026.5, so it cannot be relied on for audience binding.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

.env.example

@@ -35,6 +35,12 @@ OIDC_CLIENT_ID_WEB=replace-me
 OIDC_CLIENT_SECRET_WEB=replace-me
 OIDC_CLIENT_ID_MCP=replace-me
 OIDC_AUDIENCE=shared-memory
+# Scope whose IdP mapping emits `aud: <OIDC_AUDIENCE>`. Advertised in
+# /.well-known/oauth-protected-resource so MCP clients request it — without
+# that, Authentik never evaluates the mapping and every token 401s with
+# "claim invalid: aud". Defaults to aud-<OIDC_AUDIENCE>; set only if you
+# named the scope mapping something else.
+#OIDC_AUDIENCE_SCOPE=aud-shared-memory
 
 # -----------------------------------------------------------------------------
 # Database (Postgres 16 + pgvector — pgvector/pgvector:pg16 image)

README.md

@@ -144,6 +144,7 @@ Copy `.env.example` and fill in the values below.
 | `OIDC_CLIENT_SECRET_WEB` | both | Client secret of the Web-UI client. |
 | `OIDC_CLIENT_ID_MCP` | both | Client ID of the MCP resource-server client in your IdP. |
 | `OIDC_AUDIENCE` | both | Audience string the MCP access token must carry in its `aud` claim. Recommended: `shared-memory`. |
+| `OIDC_AUDIENCE_SCOPE` | optional | Name of the IdP scope whose mapping emits that `aud` claim. Advertised in `scopes_supported` so clients request it. Defaults to `aud-<OIDC_AUDIENCE>`. |
 | `POSTGRES_USER` / `POSTGRES_PASSWORD` / `POSTGRES_DB` | both | Local Postgres credentials. |
 | `NEXTAUTH_SECRET` | both | Session-cookie signing key. Generate with `openssl rand -base64 32`. |
 | `EMBEDDER_URL` | both | Phase 2 embedder sidecar. Leave empty in Phase 1. |
@@ -297,16 +298,33 @@ The MCP endpoint requires the access token's `aud` claim to equal
 reliable pattern:
 
 1. Create a **scope mapping** (Customisation → Property Mappings → Create →
-   Scope Mapping) named `aud-shared-memory` with expression:
+   Scope Mapping) named `aud-shared-memory`, **scope name** `aud-shared-memory`,
+   with expression:
    ```python
    return {"aud": "shared-memory"}
    ```
-2. On the MCP provider, add this scope mapping under **Scopes** and tick it
+2. On the MCP provider, add this scope mapping under **Scopes**.
-   so it's emitted for the default scope.
+3. Make sure the app advertises that scope name. It is derived automatically
+   as `aud-<OIDC_AUDIENCE>`; override with `OIDC_AUDIENCE_SCOPE` if you named
+   the mapping differently.
 
-> If you skip this, the MCP route will return 401 with
+> **Attaching the mapping is not sufficient.** Authentik evaluates a scope
-> `error_description="claim invalid: aud"`. Check `docker compose logs app`
+> mapping only when the client explicitly *requests* that scope, and an MCP
-> for the exact failure.
+> client only requests the scopes listed in `scopes_supported` from
+> `/.well-known/oauth-protected-resource`. If the audience scope isn't
+> advertised there, the mapping silently never runs, the access token carries
+> no `aud`, and every MCP call fails with 401
+> `error_description="claim invalid: aud"` — even though the OAuth handshake,
+> consent, and PKCE all succeeded. Verify with:
+>
+> ```bash
+> curl -s https://memory.example.com/.well-known/oauth-protected-resource \
+>   | jq .scopes_supported     # must include aud-<your audience>
+> ```
+>
+> Note also that Claude Code sends an RFC 8707 `resource` parameter on the
+> authorize request; Authentik 2026.5 ignores it, so it cannot be relied on
+> for audience binding. The scope mapping is what sets `aud`.
 
 Then create an **Application** for the MCP provider (same as Step A), slug
 e.g. `shared-memory-mcp`.

apps/web/app/.well-known/oauth-protected-resource/route.ts

@@ -12,10 +12,18 @@ export const dynamic = "force-dynamic";
  */
 export function GET() {
   const resource = env().PUBLIC_URL.replace(/\/$/, "");
+
+  // The audience scope MUST be advertised. Authentik only evaluates a scope
+  // mapping when the client requests that scope by name, and the client only
+  // learns scope names from this document. Omit it and every access token
+  // arrives without `aud`, which jwt.ts rejects as "claim invalid: aud".
+  const audienceScope =
+    env().OIDC_AUDIENCE_SCOPE ?? `aud-${env().OIDC_AUDIENCE}`;
+
   return NextResponse.json({
     resource,
     authorization_servers: [env().OIDC_ISSUER],
-    scopes_supported: ["openid", "profile", "email"],
+    scopes_supported: ["openid", "profile", "email", audienceScope],
     bearer_methods_supported: ["header"],
     resource_documentation: `${resource}/`,
   });

apps/web/lib/env.ts

@@ -18,6 +18,17 @@ const envSchema = z.object({
   OIDC_CLIENT_ID_MCP: z.string().min(1),
   OIDC_AUDIENCE: z.string().min(1),
 
+  // Name of the IdP scope whose mapping emits `aud: <OIDC_AUDIENCE>`.
+  //
+  // Most IdPs (Authentik included) only evaluate a scope mapping when the
+  // client actually requests that scope. The MCP client learns which scopes
+  // to request from `scopes_supported` in our protected-resource metadata,
+  // so this name has to be advertised there or the mapping never runs and
+  // every token arrives without an `aud` claim (-> 401 "claim invalid: aud").
+  //
+  // Defaults to the `aud-<audience>` convention used in the README setup.
+  OIDC_AUDIENCE_SCOPE: z.string().min(1).optional(),
+
   // Database
   DATABASE_URL: z.string().url(),