Test-DCR-MCP-Server

🇩🇪 Deutsche Version: README.de.md

A minimal, spec-compliant remote MCP server with a built-in OAuth 2.1 authorization server including Dynamic Client Registration (DCR) — built so that Notion Custom Agents can connect via "Sign in with OAuth", without ever pasting a bearer token.

Reference implementation / test server — not production-hardened. In-memory state, plaintext env passwords, no user management. See Known limits.

Why this exists

Notion Custom Agents accept custom MCP servers over OAuth only if the server supports DCR — otherwise Notion would have to pre-register a client, which it only does for official connectors. This repo is a working, verified reference for that path, including measured findings from a real Notion E2E test (see below) and optional SSO federation to Google / Microsoft Entra — the pattern you need for "connect Notion to your corporate IdP".

Features

• MCP Streamable HTTP at POST /mcp (stateless, no session store)
• Hand-rolled OAuth 2.1 authorization server (for maximum log transparency):
  • RFC 9728 Protected Resource Metadata (/.well-known/oauth-protected-resource, plus the /mcp path variant)
  • RFC 8414 Authorization Server Metadata (/.well-known/oauth-authorization-server + /openid-configuration alias)
  • RFC 7591 Dynamic Client Registration (POST /register, public clients)
  • PKCE enforced with S256 (RFC 7636)
  • Authorization code grant + refresh token grant with rotation
  • RFC 8707 resource parameter accepted and logged
  • RFC 9207 iss parameter in authorization responses
• Login form with email + password at /authorize (users provisioned via USERS_JSON)
• SSO: external identity providers switchable via env — Google and Microsoft Entra (single tenant) over OIDC (authorization code + PKCE, id_token verified via JWKS), optional domain/email allowlist
• Access tokens = JWT (HS256, self-contained); refresh tokens = opaque with rotation
• 401 + WWW-Authenticate: Bearer … resource_metadata=… on unauthenticated /mcp requests (Notion's discovery trigger)
• Request logging on all auth endpoints (JSON lines, secrets redacted) — shows exactly what Notion sends
• State file persistence (optional): DCR clients + refresh tokens survive restarts (STATE_FILE + volume)
• Server icon: /.well-known/mcp.json (Notion's discovery convention) + serverInfo.icons (SEP-973)
• Tools: whoami (identity passthrough), echo, slow_task (timeout behavior)

Quickstart (local)

cp .env.example .env
# adjust secrets in .env (min. 32 chars each), e.g.: openssl rand -base64 48
npm install
npm run dev

Server runs at http://localhost:3000.

Configuration (env)

Variable	Default	Description
BASE_URL	–	Public URL without trailing slash. Must match exactly (issuer match). Locally http://localhost:3000, in production https://…
PORT	3000	Listen port
TOKEN_SECRET	–	JWT signature (HS256), min. 32 chars
SESSION_SECRET	–	HMAC signature of the login cookie, min. 32 chars
USERS_JSON	–	Test users, e.g. [{"email":"a@b.c","password":"pw","name":"Ada"}] (plaintext — test server!). Only required when AUTH_PROVIDERS includes local
ACCESS_TOKEN_TTL	3600	Seconds. 60 = test the refresh flow quickly
REFRESH_TOKEN_TTL	2592000	Seconds (30 days)
STATE_FILE	(off)	Path to state file (DCR clients + refresh tokens). Without it: pure in-memory
SERVER_NAME	test-dcr-mcp-server	Display name: serverInfo.name, mcp.json, PRM resource_name, HTML pages
AUTH_PROVIDERS	local	Comma list: local, google, entra — combinable, e.g. local,google
GOOGLE_CLIENT_ID / GOOGLE_CLIENT_SECRET	–	Required for google
ENTRA_CLIENT_ID / ENTRA_CLIENT_SECRET / ENTRA_TENANT_ID	–	Required for entra
SSO_ALLOWED_DOMAINS	(off)	Comma list of allowed email domains for SSO
SSO_ALLOWED_EMAILS	(off)	Comma list of allowed individual addresses for SSO

SSO: external identity providers (Google / Microsoft Entra)

The server remains the OAuth issuer toward Notion (DCR, its own JWTs — unchanged). Only the login step is delegated to the IdP (federated broker pattern):

Notion ──OAuth──> this server ──OIDC──> Google / Entra
        (unchanged)            (authentication only,
                                no upstream token needed)

Flow: login page shows buttons → GET /auth/<provider>/start?txn=… → redirect to IdP (authorization code + PKCE S256 + nonce) → GET /auth/<provider>/callback → code exchange → id_token verified via JWKS (iss, aud, nonce) → allowlist check → then exactly the same path as the local login (session cookie, own code, own tokens). whoami shows the IdP (idp: "google" | "entra" | "local").

⚠️ Without SSO_ALLOWED_DOMAINS/SSO_ALLOWED_EMAILS, any account of the IdP can log in (boot warning). With Entra single tenant, the tenant already scopes the org — the allowlist is optional there.

Setting up Google

1. Google Cloud Console → pick/create project → APIs & Services → OAuth consent screen (External, basic info).
2. Credentials → Create Credentials → OAuth client ID → type Web application.
3. Authorized redirect URI: https://<host>/auth/google/callback
4. Env: GOOGLE_CLIENT_ID, GOOGLE_CLIENT_SECRET, AUTH_PROVIDERS=local,google (or without local).

Setting up Microsoft Entra (single tenant, recommended)

1. Entra Portal → Identity → Applications → App registrations → New registration.
2. Any name, Supported account types: "Accounts in this organizational directory only (Single tenant)" — only members of your tenant can log in.
3. Redirect URI: platform Web, https://<host>/auth/entra/callback.
4. Certificates & secrets → New client secret → copy the value immediately.
5. Env: ENTRA_TENANT_ID (Directory/tenant ID from the app overview page), ENTRA_CLIENT_ID, ENTRA_CLIENT_SECRET, AUTH_PROVIDERS=local,entra.
6. No additional API permissions needed (openid email profile suffices; default consent).
7. Note: the email claim is not guaranteed on Entra — the server falls back to preferred_username/upn.

Plugging in your own login (the replacement seam)

Login methods are deliberately swappable — for later projects with an existing login (e.g. app session, other SSO):

1. Produce an AuthnIdentity ({email, name, idp}, src/authn/identity.ts) from your own authentication.
2. Call completeAuthorization(res, pending, identity) (src/oauth/complete.ts) — that's the only seam. Everything after it (code, tokens, JWT, MCP) stays unchanged.

The built-in methods live in src/authn/ (local form in loginPage.ts + POST /authorize in src/oauth/authorize.ts, SSO in src/authn/idp/) and can be replaced wholesale. Want another IdP? An IdpProvider object (src/authn/idp/types.ts) plus a registry entry is enough.

Verification with curl

Or as a ready-made script (covers all steps below):

./scripts/test-flow.sh http://localhost:3000 test@example.com test1234

1. Discovery trigger: 401 with WWW-Authenticate

curl -i -X POST http://localhost:3000/mcp \
  -H 'Content-Type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}'
# → 401 Unauthorized
# → WWW-Authenticate: Bearer error="invalid_token", …, resource_metadata="http://localhost:3000/.well-known/oauth-protected-resource"

2. Well-known documents (public)

curl -s http://localhost:3000/.well-known/oauth-protected-resource | jq
curl -s http://localhost:3000/.well-known/oauth-protected-resource/mcp | jq   # RFC 9728 §3.1
curl -s http://localhost:3000/.well-known/oauth-authorization-server | jq
curl -s http://localhost:3000/.well-known/openid-configuration | jq           # alias
curl -s http://localhost:3000/.well-known/mcp.json | jq                       # Notion discovery (icon, name)

3. DCR

curl -i -X POST http://localhost:3000/register \
  -H 'Content-Type: application/json' \
  -d '{"redirect_uris":["http://localhost:9999/cb"],"client_name":"curl-test","token_endpoint_auth_method":"none","grant_types":["authorization_code","refresh_token"],"response_types":["code"]}'
# → 201 Created + {"client_id":"…", …}

4. Full PKCE flow

CID="<client_id from step 3>"
verifier=$(openssl rand -base64 96 | tr -dc 'a-zA-Z0-9-._~' | head -c 64)
challenge=$(printf %s "$verifier" | openssl dgst -sha256 -binary | base64 | tr '+/' '-_' | tr -d '=')

# Fetch login form (keep the cookie jar!)
curl -s -c jar "http://localhost:3000/authorize?response_type=code&client_id=$CID\
&redirect_uri=http%3A%2F%2Flocalhost%3A9999%2Fcb&state=xyz\
&code_challenge=$challenge&code_challenge_method=S256\
&resource=http%3A%2F%2Flocalhost%3A3000%2Fmcp"
# → HTML form; extract txn from the hidden field:
TXN=$(…)

# Submit credentials → 302 with code (+ iss, RFC 9207)
curl -s -o /dev/null -w '%{redirect_url}' -b jar -c jar -X POST http://localhost:3000/authorize \
  -d "txn=$TXN&email=test@example.com&password=test1234"
# → http://localhost:9999/cb?code=…&state=xyz&iss=…

# Exchange code → tokens
curl -s -X POST http://localhost:3000/token \
  -d "grant_type=authorization_code&code=$CODE&redirect_uri=http%3A%2F%2Flocalhost%3A9999%2Fcb\
&client_id=$CID&code_verifier=$verifier&resource=http%3A%2F%2Flocalhost%3A3000%2Fmcp"
# → {"access_token":"…","token_type":"Bearer","expires_in":60,"refresh_token":"…","scope":"mcp"}

5. MCP with token

# Important: the Accept header must include BOTH types (Streamable HTTP requirement)
curl -s -X POST http://localhost:3000/mcp \
  -H "Authorization: Bearer $AT" \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json, text/event-stream' \
  -d '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"whoami","arguments":{}}}'
# → SSE: identity of the logged-in user (email, name, idp, notionUserId, clientId, scopes, expiresAt)

6. Refresh flow (with ACCESS_TOKEN_TTL=60)

sleep 65
curl -si -X POST http://localhost:3000/mcp -H "Authorization: Bearer $AT" …   # → 401 invalid_token
curl -s -X POST http://localhost:3000/token \
  -d "grant_type=refresh_token&refresh_token=$RT&client_id=$CID"             # → new token pair (rotation!)
curl -s -X POST http://localhost:3000/token \
  -d "grant_type=refresh_token&refresh_token=$RT&client_id=$CID"             # → invalid_grant (old token consumed)

MCP Inspector (best error messages, same flow as Notion)

npx @modelcontextprotocol/inspector@latest
# UI: http://localhost:6274 → transport: "Streamable HTTP" → URL: http://localhost:3000/mcp
# → Guided OAuth flow: the Inspector does DCR itself (watch the log for its redirect_uris:
#   http://127.0.0.1:6274/oauth/callback), opens the login form, exchanges the code.

Docker

docker build -t test-dcr-mcp .
docker run --rm -p 3000:3000 --env-file .env \
  -e STATE_FILE=/data/state.json -v mcp-data:/data \
  test-dcr-mcp

Multi-stage build (node:22-alpine), non-root (USER node), HEALTHCHECK on /health, VOLUME /data for the state file.

HTTPS tunnel (Notion requires public HTTPS)

cloudflared tunnel --url http://localhost:3000
# → https://<random>.trycloudflare.com
# Restart the server with BASE_URL=https://<random>.trycloudflare.com (issuer match!)

Deploying on EasyPanel

1. Push the repo to GitHub (Dockerfile is at the root).
2. EasyPanel → Create Service → App → connect the Git repo → the Dockerfile is detected automatically.
3. Set env: BASE_URL=https://<app>.<domain>, TOKEN_SECRET, SESSION_SECRET (≥32 chars each), USERS_JSON, ACCESS_TOKEN_TTL=60 (for testing), STATE_FILE=/data/state.json.
4. Create a volume → mount path /data (persists DCR clients + refresh tokens across redeploys).
5. Assign a domain, enable HTTPS (Traefik + Let's Encrypt automatic), container port 3000.
6. Deploy → verify: curl https://<domain>/health + both well-known docs.

Connecting Notion

Prerequisite: an owner/admin has enabled Custom MCP servers (Settings → Notion AI → AI connectors → Enable Custom MCP servers).

1. Settings → Notion AI → AI connectors → Custom MCP servers → add the server by URL: https://<domain>/mcp — enter the URL in full, including /mcp! (Notion uses the entered URL as the MCP endpoint; with the root URL, traffic lands on POST / → 404 — see "Findings" below.)
2. A "Sign in with OAuth" button appears (no token field).
3. Click → browser → login form (email/password from USERS_JSON) → redirect back.
4. The server appears under All sources → MCP servers; whoami returns the identity of the signed-in user (email/name from USERS_JSON) plus the notionUserId of the connecting Notion account.
5. Tools appear lazily: Notion only calls tools/list when an agent actually uses the source. Test prompt: "Which tools does the Test-DCR-MCP-Server provide? Then call the whoami tool."

Watch the server log (all JSON lines): the initial 401, PRM fetch, AS metadata fetch, the DCR body with Notion's real redirect_uris, authorize/login, token exchange — and after 60s (with ACCESS_TOKEN_TTL=60) Notion's automatic refresh.

Spec status & outlook (MCP 2026-07-28)

This server speaks wire revision 2025-06-18/2025-11-25 (via @modelcontextprotocol/sdk v1) — that's what Notion understands today, and v1 keeps receiving fixes for at least 6 months. Spec revision 2026-07-28 has been released; assessment for this project:

• Stateless is now the spec's direction — this server is already built that way (sessionIdGenerator: undefined, fresh instance per request). The biggest breaking changes (sessions/handshake/SSE resumability removal) don't affect us.
• RFC 9207 (iss in authorization responses) is implemented — in both the code redirect and error redirects.
• DCR (RFC 7591) is deprecated in favor of Client ID Metadata Documents (CIMD). It remains available for backwards compatibility, and Notion currently only speaks DCR — this server stays the working path. Long-term, CIMD would make /register + the client store obsolete (less state, not more) — a sensible follow-up feature once clients (Inspector/Notion) speak CIMD.
• SDK v2 (scoped packages: @modelcontextprotocol/server, official Express/Fastify/Hono adapters, createMcpHandler serving both revisions at one endpoint, v1→v2 codemod): migrate after stable release; for Fastify ports the official adapter covers the previous reply.raw manual work.

Findings from the real Notion E2E test (measured, not guessed)

Everything below comes from request logs of an actual connect with Notion Custom Agents (as of 2026-08):

Discovery & DCR

• DCR without pre-registration works. Notion self-registers with client_name: "Notion", token_endpoint_auth_method: "none", scope mcp.
• Notion's redirect URI: https://app.notion.com/workflows/mcp/oauth/callback
• User agent of server-side calls: Notion-MCP-Client/1.0.
• /.well-known/mcp.json is Notion's discovery convention (name, description, icon, endpoint) and is fetched when connecting — this server serves the document including icon (self-hosted at /icon.png, generated via scripts/generate-icon.mjs). Additionally, serverInfo carries an icons array (MCP spec 2025-11-25, SEP-973) — that's how the icon in the connection dialog can be influenced without any Notion-side setting. Note: Notion appears to cache the icon per connection — disconnect and reconnect to see changes.

Authorize request — Notion sends extra parameters

response_type=code, client_id, redirect_uri, state,
code_challenge, code_challenge_method=S256,
scope=mcp, resource=<see below>,
nonce=<…>, prompt=consent,
notion_user_id=<UUID of the Notion user>

• notion_user_id is the Notion user ID of the person connecting the connector. This server passes it through as a custom notion_user_id JWT claim — whoami shows it. That lets an MCP server distinguish per Notion user even when everyone shares the same server login. (Caveat: the value arrives as a query parameter on the authorize endpoint — fine for identity experiments, would need verification for serious use.)
• nonce and prompt=consent are also sent (OIDC flavor) but don't need to be evaluated.

⚠️ Most important practical point: the entered URL IS the endpoint

• Notion uses the URL entered when creating the connector as the endpoint for all MCP traffic — and as the RFC 8707 resource parameter throughout the flow.
• If the connector is added with the root URL (https://host/), Notion sends its JSON-RPC calls to POST / — not /mcp. Symptom in the Notion agent: "Failed to connect to MCP server"; in the server log: POST / → 404 (preceded by successful token refreshes — the OAuth part works).
• Fix: enter the connector with the full URL including the path, i.e. https://host/mcp. This server deliberately serves MCP only on /mcp (no root mount), keeping the pattern clean on hosts that also serve a conventional API on /. GET / shows an HTML info page with the correct URL.
• The resource parameter follows the same rule: entered with /mcp → resource=…/mcp; root entry → resource=…/. This server accepts both and logs mismatches (learning mode).

Tool calls

• arguments is optional in the MCP spec — but de facto mandatory at two layers. On the first whoami call, the Notion LLM omitted arguments → Notion's client rejected it before sending: payload.toolArguments should be defined, instead was 'undefined' (Notion-internal field naming; the call never reached the server). Retry with arguments: {} → success.
• Server-side caution too: the MCP SDK rejects missing arguments when a tool is registered with inputSchema (-32602: expected object, received undefined) — even with an empty schema {}. Fix: register parameterless tools without inputSchema entirely (callback signature becomes (extra) => …); then the server accepts both variants. whoami is built that way here.
• After connecting, Notion also probes GET /mcp (SSE stream) → our stateless server answers 405 — Notion tolerates that and falls back to POST.
• After initialize, Notion sends notifications/initialized → response 202 (no body), normal.
• With ACCESS_TOKEN_TTL=60, Notion refreshes the token before almost every MCP call (in the log: refresh_token grant right before each POST /mcp batch). Works, but noisy — raise the TTL after testing the refresh path.

Token behavior

• Notion refreshes multiple times immediately after connecting (parallel/redundant workers) — refresh rotation must work cleanly or the connection breaks right after setup.
• Afterwards, with a short ACCESS_TOKEN_TTL (60s), the refresh grant is used as expected before further MCP calls.
• PKCE is S256, code exchange immediately after redirect. All standard-compliant.

Architecture notes

• Stateless MCP transport: fresh McpServer+StreamableHTTPServerTransport instance per POST /mcp (sessionIdGenerator: undefined). GET /mcp → 405 (no standalone SSE without sessions).
• What is stored where? Access tokens (JWT) nowhere — only signed/verified. Refresh tokens, DCR clients, auth codes, pending logins in Maps; of these, clients + refresh tokens are persisted to STATE_FILE (debounced, atomic via tmp+rename). Auth codes/pending (10-min TTL) deliberately stay volatile. Users always come from USERS_JSON.
• Login session: HMAC-signed cookie (HttpOnly; SameSite=Lax; Secure only on HTTPS) with JSON payload {email, name, idp} — works for local users and SSO identities alike; subsequent authorize requests skip the login.
• Authn layer (src/authn/): login methods (local, Google, Entra) produce an AuthnIdentity and end at the completeAuthorization seam — swappable for later projects with their own login.
• Express 5, because @modelcontextprotocol/sdk itself depends on it (no duplicate installation, the req.auth augmentation applies).

Known limits (deliberate)

• Plaintext passwords in env; password comparison without hashing.
• No rate limiting, no CSRF tokens on the login form (txn ID is random, sufficient for the test).
• resource mismatch is only logged, not rejected (learning mode).
• Without STATE_FILE, registrations/refresh tokens don't survive a restart → Notion will re-register and the user logs in again.
• SSO: email_verified is only checked for Google (on Entra we trust the tenant); without an allowlist, login is open to all accounts of the IdP.
• The SSO flow has not been tested end-to-end without a real IdP app registration (structurally tested: start redirects incl. PKCE parameters, error paths, provider deactivation).
• This is a test/reference server. Before any production use: real user management, hashed credentials, rate limiting, stricter validation, key management — or better, use it as the reference it is meant to be.

License

MIT © LOUPZ GmbH & Co. KG