fix: serve RFC 9728 path-suffixed metadata, document connector redirect URIs

Two separate discovery footguns, both found while debugging an Authentik
"Redirect URI Error" on a claude.ai custom connector.

RFC 9728 §3.1 puts the metadata for a resource identified by
`https://host/api/mcp` at `/.well-known/oauth-protected-resource/api/mcp`.
Only the root form was served, so clients that derive the metadata URL from
the MCP endpoint URL — rather than reading `resource_metadata` off our 401 —
got Next.js's HTML 404 and failed discovery with a JSON parse error.

Add a `[...path]` route serving the same document with `resource` naming the
suffixed identifier (§3.3 has the client compare it as an exact string, so
echoing the bare origin would be rejected). The document body moves to
`lib/auth/resource-metadata.ts` so the two routes cannot drift apart on
`scopes_supported` — a divergence there costs you the `aud` claim or the
refresh token. Paths are allowlisted rather than wildcarded so this cannot
advertise resources the app does not serve. `buildWwwAuthenticate()` still
points at the root URL; this change is purely additive.

Separately, the redirect URIs an MCP provider needs depend on how clients
reach it: a loopback URI for the CLI, `https://claude.ai/api/mcp/auth_callback`
for a claude.ai custom connector. Registering only the former is what produces
the "Redirect URI Error" page, and a portless `http://localhost/callback`
entry matches nothing the CLI sends. Document both, keyed on the literal
error text, and note that DCR is enterprise-gated on Authentik so these are
hand-registered on a FOSS instance.

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

README.md

@@ -298,12 +298,75 @@ tokens carry `aud: shared-memory` (or whatever value you chose).
   or `Confidential` if you prefer to issue a secret to each Claude Code
   install — both work. Phase 1 expects Public.
 - **Client ID:** auto-generated → copy to `.env` as `OIDC_CLIENT_ID_MCP`
-- **Redirect URIs:** Claude Code prints the exact value when it first
-  connects to the MCP endpoint. Paste it into Authentik then.
+- **Redirect URIs:** more than one, and which ones depends on how people
+  reach the server — see **Which redirect URIs to register** below.
 - **Scopes:** `openid`, `profile`, `email` (plus `offline_access` — see
   **Keeping sessions alive** below)
 - **Signing Key:** same cert as the Web provider
 
+#### Which redirect URIs to register
+
+The MCP provider is reached by clients of two different shapes — one running on
+your machine, one running inside claude.ai — and they come back from the IdP at
+**different** redirect URIs. Register every one you intend to use, before the
+first connection attempt:
+
+- **Claude Code CLI, including this repo's plugin** — the CLI catches the
+  callback on a loopback listener, so the URI is
+  `http://localhost:<port>/callback`, where `<port>` is whatever
+  `--callback-port` (or the plugin's `callbackPort`) is set to. Set the entry's
+  matching mode to **Regex** so any port works without re-registering:
+
+  ```
+  http://(localhost|127\.0\.0\.1):[0-9]+/.*
+  ```
+
+  **The port is not optional.** Authentik rejects a portless
+  `http://localhost/callback`, so an entry copied from the Entra ID walkthrough
+  — where the port component is ignored on purpose, see
+  [docs/oidc-entra-id.md](docs/oidc-entra-id.md) — matches nothing the CLI ever
+  sends.
+
+- **A claude.ai custom connector** — the server added through claude.ai's web
+  UI rather than installed locally. claude.ai brokers the OAuth flow, so the
+  browser never returns to your machine and the loopback entries above are
+  irrelevant. Register the exact string:
+
+  ```
+  https://claude.ai/api/mcp/auth_callback
+  ```
+
+- **The manual-paste fallback** (*C. Manual-paste fallback* below) — that
+  callback is hosted by *this* server, not by the client:
+
+  ```
+  https://memory.example.com/auth/cli-callback
+  ```
+
+> **A missing entry shows up as Authentik's "Redirect URI Error" page** — *"The
+> request fails due to a missing, invalid, or mismatching redirection URI
+> (redirect_uri)"* — served **after** the client sends you to Authentik but
+> **before** any login or consent screen. Nothing in the client says which URI
+> was rejected, so it reads as "the connector is broken" when the provider
+> simply has no entry matching what was sent. Adding the server as a claude.ai
+> connector without the `https://claude.ai/api/mcp/auth_callback` entry is the
+> common way to land here.
+>
+> **Nothing registers these for you — on a FOSS instance.** Authentik *does*
+> implement RFC 7591 Dynamic Client Registration
+> ([goauthentik/authentik#8751](https://github.com/goauthentik/authentik/issues/8751),
+> closed July 2026), but gated behind an **enterprise** licence; a maintainer
+> has since said it will move to the open-source build. Until it does, a FOSS
+> instance advertises no `registration_endpoint` at all. Check yours:
+>
+> ```
+> curl -s "${OIDC_ISSUER_MCP}.well-known/openid-configuration" | jq .registration_endpoint
+> ```
+>
+> `null` means no client — CLI or claude.ai — can add its own redirect URI, so
+> every URI above is typed into the provider by hand. (Same gap as **Why no
+> zero-config plugin yet** below.)
+
 #### Keeping sessions alive (`offline_access`)
 
 Without this, a connected MCP client gets an access token and **no refresh
@@ -413,6 +476,13 @@ prompt, never reaching the app.
 
 Three paths, in order of preference:
 
+> **Connecting from claude.ai instead?** A server added there as a *custom
+> connector* needs nothing on your machine, but its OAuth callback is
+> `https://claude.ai/api/mcp/auth_callback`, not a loopback URI. Register it on
+> the MCP provider first (**Which redirect URIs to register** above) or the
+> connector stops at Authentik's *Redirect URI Error* page before you ever see
+> a login prompt.
+
 ### A. Plugin (recommended — one command, no flags to remember)
 
 This repo doubles as a Claude Code plugin marketplace. `plugin/.mcp.json` ships a
@@ -501,8 +571,8 @@ What happens:
 `--callback-port` is required because your IdP only accepts pre-registered
 redirect URIs. Pick any free port; just make sure the matching URI is in
 your MCP client's **Redirect URIs** list. Authentik users with the regex
-pattern from the setup step (`^http://(127\.0\.0\.1|localhost):\d+/.*$`)
-can use any port without re-registering.
+entry from the setup step (`http://(localhost|127\.0\.0\.1):[0-9]+/.*`) can
+use any port without re-registering.
 
 ### C. Manual-paste fallback (when loopback isn't reachable)
 
@@ -725,6 +795,14 @@ reopen a closed question.
   scope mapping; on EntraID it's the API "Application ID URI"; on Keycloak
   it's a client-scope audience mapper. See **Setting the `aud` claim** above
   for the Authentik recipe; other IdPs need the equivalent in their UI.
+- **Authentik shows "Redirect URI Error — The request fails due to a missing,
+  invalid, or mismatching redirection URI (redirect_uri)"** — the redirect URI
+  the client sent is not registered on the `shared-memory-mcp` provider. From a
+  claude.ai custom connector the missing entry is
+  `https://claude.ai/api/mcp/auth_callback`; from the CLI it's the loopback URI
+  for your `--callback-port`, and a portless `http://localhost/callback` entry
+  will not match it. Authentik has no Dynamic Client Registration, so no client
+  can add the URI itself — see **Which redirect URIs to register** above.
 - **Auth.js callback fails with `OAUTH_CALLBACK_ERROR`** — your `PUBLIC_URL`
   doesn't match the redirect URI your IdP is configured with. They must be
   exactly equal, scheme and trailing slash included.

apps/web/app/.well-known/oauth-protected-resource/[...path]/route.test.ts

@@ -0,0 +1,86 @@
+import { afterEach, describe, expect, test, vi } from "vitest";
+
+/**
+ * RFC 9728 §3.1 puts the metadata for `https://host/api/mcp` at
+ * `https://host/.well-known/oauth-protected-resource/api/mcp`. MCP clients
+ * that derive that URL from the endpoint URL — instead of following the
+ * `resource_metadata` parameter on our 401 — used to receive the Next.js 404
+ * HTML page here, so discovery died on a JSON parse error.
+ *
+ * Two things therefore have to hold, and both are easy to break silently:
+ * the document must name the SUFFIXED resource (§3.3 has the client reject a
+ * document whose `resource` isn't the identifier it asked about), and it must
+ * stay byte-for-byte in step with the root document's scope list, because a
+ * scope missing from whichever document a given client reads is a scope that
+ * client will never request.
+ */
+
+type Metadata = { resource: string; scopes_supported: string[] };
+
+async function fetchSuffixed(
+  segments: string[],
+): Promise<{ status: number; body: Metadata }> {
+  vi.resetModules();
+  const { GET } = await import(
+    "@/app/.well-known/oauth-protected-resource/[...path]/route"
+  );
+  const res = await GET(new Request("http://localhost/ignored"), {
+    params: Promise.resolve({ path: segments }),
+  });
+  return { status: res.status, body: (await res.json()) as Metadata };
+}
+
+async function fetchRoot(): Promise<Metadata> {
+  vi.resetModules();
+  const { GET } = await import("@/app/.well-known/oauth-protected-resource/route");
+  return (await GET().json()) as Metadata;
+}
+
+afterEach(() => {
+  delete process.env.OIDC_OFFLINE_ACCESS;
+  delete process.env.OIDC_AUDIENCE_SCOPE;
+});
+
+describe("path-suffixed oauth-protected-resource metadata", () => {
+  test("serves the MCP endpoint's document with the suffixed resource identifier", async () => {
+    const { status, body } = await fetchSuffixed(["api", "mcp"]);
+
+    expect(status).toBe(200);
+    // §3.3: a strict client compares this against the identifier it asked
+    // about, so the bare origin would get the whole document rejected.
+    expect(body.resource).toBe("http://localhost:3000/api/mcp");
+  });
+
+  test("404s for a path this app does not serve, rather than advertising it", async () => {
+    // The allowlist exists so we never claim that arbitrary paths are
+    // OAuth-protected resources of this deployment.
+    const { status } = await fetchSuffixed(["api", "not-mcp"]);
+
+    expect(status).toBe(404);
+  });
+
+  test("advertises exactly the scopes the root document does", async () => {
+    // Regression guard against the two documents drifting apart: the audience
+    // scope is what makes `aud` appear on the token at all, and a client that
+    // discovered us through the suffixed URL would never request a scope that
+    // only the root document lists.
+    process.env.OIDC_OFFLINE_ACCESS = "true";
+
+    const root = await fetchRoot();
+    const { body: suffixed } = await fetchSuffixed(["api", "mcp"]);
+
+    expect(suffixed.scopes_supported).toEqual(root.scopes_supported);
+    expect(suffixed.scopes_supported).toContain("aud-test-audience");
+    expect(suffixed.scopes_supported).toContain("offline_access");
+  });
+
+  test("honours an explicit audience scope name, like the root document", async () => {
+    process.env.OIDC_AUDIENCE_SCOPE = "custom-aud-scope";
+
+    const root = await fetchRoot();
+    const { body: suffixed } = await fetchSuffixed(["api", "mcp"]);
+
+    expect(suffixed.scopes_supported).toContain("custom-aud-scope");
+    expect(suffixed.scopes_supported).toEqual(root.scopes_supported);
+  });
+});

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

@@ -0,0 +1,60 @@
+import { NextResponse } from "next/server";
+import { buildResourceMetadata, publicOrigin } from "@/lib/auth/resource-metadata";
+
+export const runtime = "nodejs";
+export const dynamic = "force-dynamic";
+
+/**
+ * Resource paths this deployment will publish metadata for.
+ *
+ * An allowlist rather than a wildcard, for two reasons. RFC 9728 §3.1 maps a
+ * metadata URL to one specific protected resource, so answering for arbitrary
+ * paths would advertise resources this app does not serve — a client could
+ * "discover" `https://host/anything` as an OAuth-protected resource and be
+ * told, wrongly, that tokens for it are obtainable from our IdP. And every
+ * path that answers is surface: a wildcard turns this into an open reflector
+ * that echoes attacker-chosen path segments back inside a JSON document.
+ *
+ * `api/mcp` is the only MCP endpoint here (app/api/mcp/route.ts). Add an
+ * entry when a second one ships — not before.
+ */
+const METADATA_RESOURCE_PATHS: ReadonlySet<string> = new Set(["api/mcp"]);
+
+/**
+ * RFC 9728 §3.1 — path-suffixed protected resource metadata.
+ *
+ * For a resource identified by `https://host/api/mcp`, the spec puts its
+ * metadata at `https://host/.well-known/oauth-protected-resource/api/mcp`:
+ * the resource's path is appended to the well-known path. Clients that derive
+ * the metadata URL from the MCP endpoint URL — rather than reading
+ * `resource_metadata` off our 401's `WWW-Authenticate` header — probe that URL
+ * first, and before this route existed they got Next.js's 404 HTML page, which
+ * fails discovery with a JSON parse error rather than anything diagnosable.
+ *
+ * The document is identical to the root one except for `resource`, which must
+ * name the suffixed identifier: §3.3 requires the client to check that the
+ * returned `resource` equals the identifier it asked about, so echoing the
+ * bare origin here would make a strict client reject the document outright.
+ */
+export async function GET(
+  _req: Request,
+  ctx: { params: Promise<{ path: string[] }> },
+): Promise<NextResponse> {
+  const { path } = await ctx.params;
+  // Segments arrive already percent-decoded and never empty, but join and
+  // compare on the same normalized form the allowlist is written in.
+  const resourcePath = path.join("/");
+
+  if (!METADATA_RESOURCE_PATHS.has(resourcePath)) {
+    // JSON, not the HTML 404 page, so a client that probes a wrong path gets
+    // a parseable answer instead of the failure mode this route exists to fix.
+    return NextResponse.json(
+      { error: "not_found", error_description: "no such protected resource" },
+      { status: 404 },
+    );
+  }
+
+  return NextResponse.json(
+    buildResourceMetadata(`${publicOrigin()}/${resourcePath}`),
+  );
+}

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

@@ -1,6 +1,5 @@
 import { NextResponse } from "next/server";
-import { env } from "@/lib/env";
-import { mcpIssuer } from "@/lib/auth/jwt";
+import { buildResourceMetadata, publicOrigin } from "@/lib/auth/resource-metadata";
 
 export const runtime = "nodejs";
 export const dynamic = "force-dynamic";
@@ -10,36 +9,12 @@ export const dynamic = "force-dynamic";
  *
  * MCP clients discover the authorization server (Authentik) via this
  * endpoint after receiving a 401 with `WWW-Authenticate: resource_metadata=...`.
+ *
+ * This is the root form of the document, describing the deployment origin as
+ * the protected resource. Clients that derive the metadata URL from the MCP
+ * endpoint URL instead of following the header land on the path-suffixed form
+ * (§3.1) served by the sibling `[...path]` route.
  */
 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}`;
-
-  // Same mechanism as the audience scope, different consequence: a client
-  // only requests `offline_access` if it sees the name here, and without
-  // that request the IdP returns no refresh token — so the client cannot
-  // renew and the user gets kicked back to an interactive login whenever
-  // the access token expires.
-  //
-  // Opt-in, because the IdP needs a matching scope mapping; advertising one
-  // it doesn't offer can fail the whole authorization request.
-  const scopes = ["openid", "profile", "email", audienceScope];
-  if (env().OIDC_OFFLINE_ACCESS) scopes.push("offline_access");
-
-  return NextResponse.json({
-    resource,
-    // The MCP application's issuer, which is not necessarily the Web UI's —
-    // see mcpIssuer(). Advertising the wrong one sends clients to a discovery
-    // document whose tokens this endpoint will then reject on `iss`.
-    authorization_servers: [mcpIssuer()],  // as configured, slash and all
-    scopes_supported: scopes,
-    bearer_methods_supported: ["header"],
-    resource_documentation: `${resource}/`,
-  });
+  return NextResponse.json(buildResourceMetadata(publicOrigin()));
 }

apps/web/lib/auth/resource-metadata.ts

@@ -0,0 +1,73 @@
+import { env } from "@/lib/env";
+import { mcpIssuer } from "@/lib/auth/jwt";
+
+/**
+ * The protected-resource metadata document, RFC 9728 §2.
+ *
+ * Shared by both metadata routes — the root `/.well-known/oauth-protected-
+ * resource` and the path-suffixed `/.well-known/oauth-protected-resource/
+ * <resource path>` form of §3.1 — because the two documents differ ONLY in
+ * the `resource` identifier they describe. Anything else drifting between
+ * them is a bug: a client that discovers us through the suffixed URL would
+ * be told to request a different scope set than one that follows the
+ * `WWW-Authenticate: resource_metadata=...` header, and whichever of the two
+ * lost the audience scope would hand back tokens with no `aud` claim.
+ */
+export interface ResourceMetadata {
+  resource: string;
+  authorization_servers: string[];
+  scopes_supported: string[];
+  bearer_methods_supported: string[];
+  resource_documentation: string;
+}
+
+/**
+ * The public origin, with any trailing slash stripped.
+ *
+ * `resource` values are compared as exact strings by clients (RFC 9728 §3.3),
+ * so `https://host/` and `https://host` are not interchangeable — PUBLIC_URL
+ * is written both ways in the wild and only the stripped form is emitted.
+ */
+export function publicOrigin(): string {
+  return env().PUBLIC_URL.replace(/\/$/, "");
+}
+
+/**
+ * Build the metadata document for `resource`.
+ *
+ * The caller supplies the resource identifier because it depends on which
+ * URL the document was fetched from; everything else is deployment config.
+ */
+export function buildResourceMetadata(resource: string): ResourceMetadata {
+  // The audience scope MUST be advertised. Authentik only evaluates a scope
+  // mapping when the client requests that scope by name, and the client only
+  // learns scope names from this document. Omit it and every access token
+  // arrives without `aud`, which jwt.ts rejects as "claim invalid: aud".
+  const audienceScope =
+    env().OIDC_AUDIENCE_SCOPE ?? `aud-${env().OIDC_AUDIENCE}`;
+
+  // Same mechanism as the audience scope, different consequence: a client
+  // only requests `offline_access` if it sees the name here, and without
+  // that request the IdP returns no refresh token — so the client cannot
+  // renew and the user gets kicked back to an interactive login whenever
+  // the access token expires.
+  //
+  // Opt-in, because the IdP needs a matching scope mapping; advertising one
+  // it doesn't offer can fail the whole authorization request.
+  const scopes = ["openid", "profile", "email", audienceScope];
+  if (env().OIDC_OFFLINE_ACCESS) scopes.push("offline_access");
+
+  return {
+    resource,
+    // The MCP application's issuer, which is not necessarily the Web UI's —
+    // see mcpIssuer(). Advertising the wrong one sends clients to a discovery
+    // document whose tokens this endpoint will then reject on `iss`.
+    authorization_servers: [mcpIssuer()],  // as configured, slash and all
+    scopes_supported: scopes,
+    bearer_methods_supported: ["header"],
+    // Documentation lives at the site root regardless of which resource this
+    // document describes, so it is always derived from the public origin and
+    // not from `resource`.
+    resource_documentation: `${publicOrigin()}/`,
+  };
+}

docs/oidc-entra-id.md

@@ -231,13 +231,17 @@ https://memory.example.com/auth/cli-callback
 The first covers the loopback listener from README → *B. OAuth flow*; the
 second is the manual-paste fallback from *C*. "Mobile and desktop
 applications" permits arbitrary `https://` URIs alongside the loopback one, so
-both live on the same platform.
+both live on the same platform. If the server will also be added as a claude.ai
+custom connector, that flow is brokered by claude.ai and comes back to
+`https://claude.ai/api/mcp/auth_callback` — register it here too, or the
+connector stops at the IdP's redirect-URI mismatch error before any login
+prompt. See README → *Which redirect URIs to register*.
 
 **Note the missing port.** Entra ignores the port component when matching
 `http://localhost` redirect URIs, so the single registration
 `http://localhost/callback` matches `http://localhost:33418/callback`,
 `http://localhost:9999/callback`, and any other port. This is Entra's
-equivalent of the Authentik regex (`^http://(127\.0\.0\.1|localhost):\d+/.*$`)
+equivalent of the Authentik regex (`http://(localhost|127\.0\.0\.1):[0-9]+/.*`)
 the README mentions — users can pick any `--callback-port` without
 re-registering.
 

terraform/README.md

@@ -72,6 +72,16 @@ The redirect URI you register on the Web UI client is
 `https://${domain_name}/api/auth/callback/oidc`, so plan the domain name
 *before* configuring the IdP.
 
+The MCP client needs its own list, and most of it does not depend on the
+domain: a loopback URI for the Claude Code CLI, plus
+`https://claude.ai/api/mcp/auth_callback` if anyone will add the server as a
+claude.ai custom connector. Only the manual-paste fallback,
+`https://${domain_name}/auth/cli-callback`, follows the domain. See
+[Which redirect URIs to register](../README.md#which-redirect-uris-to-register)
+— a client can only register its own redirect URI against an IdP that offers
+Dynamic Client Registration, which Authentik gates behind an enterprise
+licence, so plan on adding all of these by hand.
+
 ---
 
 ## Quick start