mcp-oauth2-proxy

- Interactiveauthorization_code+ PKCEflow with a built-in local browser callback listener — no manual code copy/paste.
- Refresh-token cacheon disk (AES‑256‑GCM,0600), so the browser only opens once per machine.
- client_credentialsgrant for headless / service-to-service use.
- RFC 9728 + RFC 8414 discoveryof token and authorization endpoints from the upstream — usually zero OAuth config required.
- Proactive token refreshwith skew, in-flight de-duplication, and a 401 → invalidate → retry loop.
- Streamable-HTTPupstream support: single-shot JSON, SSEtext/event-streamresponses, and the optional long-lived server-notification channel. HonorsMcp-Session-Id.
- Stderr-only logging(pino) with redaction of tokens, secrets, andAuthorizationheaders — stdout stays a clean JSON-RPC channel.
- Discovery.Optionally fetch RFC 9728/8414 metadata to fill intokenUrl,authorizationUrl,scope, andresource.
- Token manager.Wrap the configuredGrantwith caching, refresh-skew, in-flight dedup, and 401 invalidation.
- Prefetch.CallgetToken()once at startup so the interactive browser flow (if needed) happens before the first MCP message arrives.
- Bridge.For each stdin JSON-RPC line, POST toupstream.urlwith aBearertoken; single-shot JSON responses become one stdout line, SSE responses one line per event. A401triggersinvalidate()and a single retry.
- Server stream.Afterinitialize, optionally hold open aGET text/event-streamchannel for server-initiated notifications.

You don't need to install anything — MCP clients can launch the proxy directly vianpx:

For development against a local checkout:

git clone https://github.com/ChengleiYuan/mcp-oauth2-proxy.git cd mcp-oauth2-proxy npm install npm run build

Interactive login (recommended for end users)

UPSTREAM_URL=https://mcp.example.com/mcp \ OAUTH2_GRANT=authorization_code \ OAUTH2_CLIENT_ID=<your-client-id> \ npx -y mcp-oauth2-proxy

UPSTREAM_URL=https://mcp.example.com/mcp \ OAUTH2_GRANT=client_credentials \ OAUTH2_TOKEN_URL=https://idp.example.com/oauth2/token \ OAUTH2_CLIENT_ID=my-service \ OAUTH2_CLIENT_SECRET='…' \ OAUTH2_SCOPE='mcp:read mcp:write' \ npx -y mcp-oauth2-proxy

- Tokens are acquired by the proxy itself; the upstreamAuthorizationheader is always set by the proxy, never passed through from the client.
- Access tokens live in memory only. Refresh tokens are cached encrypted (AES‑256‑GCM, key file mode0600) — honest obfuscation against casual disk reads,notprotection against a process running as the same OS user.
- Cleartexthttp://to non-loopback hosts isrejected at startup(override withALLOW_INSECURE_HTTP=true);https://and loopbackhttp://are always allowed. The interactive callback listener validates theHostheader to defeat DNS-rebinding.
- All logs go to stderr with tokens, secrets, andAuthorizationheaders redacted; stdout is reserved for JSON-RPC.

npm install npm run build # compile TS to dist/ npm run dev # tsx watch npm test # vitest (unit + integration)

- Multiple upstream MCP servers per process
- OS-keychain-backed refresh-token storage (DPAPI / Keychain / libsecret)
- mTLS / JWT-bearer / device-code / ROPC grants
- HTTP / SSE inbound transport (this is a stdio MCP server)

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