MCP Stdio
Stdio-to-HTTP gateway — connects MCP clients to remote HTTP MCP servers
Open source Open in the app JSON README (API)
About
Stdio-to-HTTP gateway — connects MCP clients to remote HTTP MCP servers
Details
- Kind
- MCP servers
- Topic
- No topic detected
- Publisher
- shigechika
- Origin
- official
- Category
- ferramentas
- Transport
- local
- Version
- 0.43.6
- Stars
- 8
- Forks
- 1
- Last push
- 2026-08-23T14:25:14Z
- Repository state
- ativo
- Language
- Python
- License
- MIT
- Added
- 2026-08-29 04:01:23
- Updated
- 2026-08-29 04:01:23
- Origin id
io.github.shigechika/mcp-stdio
README
<!-- mcp-name: io.github.shigechika/mcp-stdio -->
# mcp-stdio
English | [日本語](README.ja.md)
A stdio↔HTTP MCP gateway that works in **both directions** — the same
binary is both an MCP-over-HTTP **client** gateway and, via `serve` mode, a
full MCP-over-HTTP **server** (with an optional embedded OAuth 2.1
Authorization Server), so it can sit on either end of an MCP connection.
📖 **New here? Start with the [user guide](https://shigechika.github.io/mcp-stdio/)** — task-oriented docs for connecting a client or publishing a server. This README is the full reference.
## Overview
**Client gateway (default mode) — stdio → HTTP.** [MCP](https://modelcontextprotocol.io/) clients like Claude Desktop and Claude Code see mcp-stdio as a locally running self-hosted MCP server, while it relays all requests to a remote MCP server with support for various authentication methods:
```mermaid
flowchart BT
A[Claude<br>Desktop/Code] <-- stdio --> B(mcp-stdio)
B <== "<b>HTTPS</b><br>Streamable HTTP / SSE<br>Bearer Token<br>Header<br>OAuth" ==> C[Remote<br>MCP Server]
B -. "OAuth 2.1<br>(PKCE)" .-> D[Authorization<br>Server]
D -. callback .-> B
style B fill:#4a5,stroke:#333,color:#fff
```
Bearer tokens, custom headers, and OAuth 2.1 credentials are forwarded to the remote server.
**Reverse gateway (`mcp-stdio serve`) — HTTP → stdio.** The mirror image: takes a
local stdio MCP server (any language, any framework) and exposes it as a
Streamable HTTP endpoint, with optional bearer-token or embedded-OAuth-2.1
authentication, per-user backend isolation when OAuth is enabled, and a
restart-durable token store —
see [Reverse gateway: `serve` mode](#reverse-gateway-serve-mode) below. This
is how mcp-stdio can stand in for a framework's own HTTP/OAuth hosting layer
(e.g. instead of depending on a Python web framework's built-in server for
just that part) when the tool definitions themselves already run fine over
stdio.
## Features
- **Both MCP transports supported** — Streamable HTTP (current spec, default) and SSE (MCP 2024-11-05 legacy), selectable with `--transport`. SSE parser follows the [WHATWG Server-Sent Events spec](https://html.spec.whatwg.org/multipage/server-sent-events.html).
- **OAuth 2.1 client** — built-in authorization code flow with PKCE, dynamic client registration, token refresh, and secure token persistence. Implements the full MCP authorization spec at the section level:
- [RFC 9728](https://www.rfc-editor.org/rfc/rfc9728) Protected Resource Metadata
- §3 discovery of authorization servers via `/.well-known/oauth-protected-resource`
- §3.1 path-aware well-known URL construction for path-based reverse-proxy deployments, with host-root fallback; preserves the resource URL's query component on the constructed metadata URL
- §3.3 `resource` field validation — warn on mismatch, continue
- §5.1 `WWW-Authenticate: Bearer resource_metadata=` hint — probes the server before discovery so servers that publish PRM at a non-standard URL are found without well-known path guessing
- [RFC 8414](https://www.rfc-editor.org/rfc/rfc8414) Authorization Server Metadata
- §3.1 well-known URL construction, including path insertion for issuers with path components
- §3.3 `issuer` validation — reject a cross-origin issuer (AS mix-up guard), warn on a same-origin mismatch (trailing slash / path / case) and continue
- §3 OpenID Connect Discovery 1.0 fallback — when the OAuth well-known 404s, probe `/.well-known/openid-configuration` (path-append and path-insertion) for ASes that expose only the OIDC form (Auth0, Okta, Azure AD, Google)
- [RFC 8707](https://www.rfc-editor.org/rfc/rfc8707) Resource Indicators
- §2 `resource` parameter in authorization, token exchange, **and refresh** requests
- [RFC 7636](https://www.rfc-editor.org/rfc/rfc7636) PKCE
- §4.1–4.2 S256 `code_challenge_method` with an 86-char `code_verifier`
- [RFC 8628](https://www.rfc-editor.org/rfc/rfc8628) Device Authorization Grant
- §3.1 device authorization request with `resource` indicator (RFC 8707)
- §3.4–3.5 token polling with `authorization_pending` / `slow_down` (interval +=5 s) / `expired_token` / `access_denied` handling
- DCR registers `urn:ietf:params:oauth:grant-type:device_code` in `grant_types` (RFC 7591 §2)
- [RFC 7591](https://www.rfc-editor.org/rfc/rfc7591) Dynamic Client Registration
- §3 client registration request; `token_endpoint_auth_method` chosen from `token_endpoint_auth_methods_supported` in AS metadata (prefers `none` → `client_secret_post` → `client_secret_basic`)
- §3.2.1 `client_secret_expires_at` handling — auto re-register on expiry
- `application_type: "native"` in DCR ([RFC 8252](https://www.rfc-editor.org/rfc/rfc8252) §8.4 / MCP SEP-837): the loopback auth-code and headless device flows are native clients, so the loopback redirect is not rejected as the RFC 7591 default `"web"`
- [Client ID Metadata Documents](https://modelcontextprotocol.io/specification/2025-11-25/basic/authorization#client-id-metadata-documents) (MCP 2025-11-25 / [draft-ietf-oauth-client-id-metadata-document-00](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-client-id-metadata-document-00))
- `--client-metadata-url` presents an operator-hosted HTTPS document URL as `client_id`, skipping Dynamic Client Registration; honoured when set even if the AS metadata does not (yet) advertise `client_id_metadata_document_supported` (warns instead of silently falling back), and outranked by a pre-registered `client_id` (`--client-id` or `MCP_OAUTH_CLIENT_ID`) (#60)
- the hosted document's `redirect_uris` must include mcp-stdio's loopback callback **without a port** (`http://127.0.0.1/callback`) — the actual callback binds a fresh ephemeral port every run, and the AS must accept any port for a loopback redirect URI ([RFC 8252](https://www.rfc-editor.org/rfc/rfc8252) §7.3 / §8.4)
- [RFC 6749](https://www.rfc-editor.org/rfc/rfc6749) OAuth 2.0
- §2.3.1 `client_secret_basic`: `Authorization: Basic` header with percent-encoded credentials (applied to code exchange, token refresh, and Device Authorization Grant polling)
- [RFC 6750](https://www.rfc-editor.org/rfc/rfc6750) Bearer Token usage
- §2.1 `Authorization: Bearer <token>` request header
- **Works with MCP 2026-07-28 servers** — add `--protocol-era auto` and mcp-stdio asks the server which protocol it speaks and adapts; your MCP client needs no changes. Without the flag nothing changes, so upgrading is safe. `mcp-stdio serve` answers both old and new clients on the same address automatically — or only the newer ones with `--modern-only`, and `--modern-idle-ttl` reclaims idle backends. Newer clients can also hold one connection open and hear when your server's tool, prompt or resource lists change, or when a specific resource they named is updated (mcp-stdio subscribes on their behalf when your server declares `resources.subscribe`). Verified end to end against python-sdk v2.0.0 in both directions. → [Working with MCP 2026-07-28 servers](https://shigechika.github.io/mcp-stdio/modes/#protocol-eras)
- **Retry with backoff** — retries up to 3 times on connection errors
- **HTTP 429 / 503 handling** — honours `Retry-After` (delta-seconds or HTTP-date) up to a 60-second cap on both 429 (Too Many Requests) and 503 (Service Unavailable) — the two spec-sanctioned Retry-After carriers (RFC 9110 §10.2.3) — then surfaces the status so the client can decide (cf. modelcontextprotocol/typescript-sdk#1892)
- **Auto-pagination** (Streamable HTTP transport) — transparently follows `nextCursor` for `tools/list` / `resources/list` / `resources/templates/list` / `prompts/list` and merges the pages into one response, so clients that drop pages beyond the first still see the full list (cf. anthropics/claude-code#39586)
- **Streaming resilience** — streams SSE responses in real time; auto-reconnects on mid-stream disconnect
- **Line-separator safety** — escapes raw `U+2028` / `U+2029` (legal in JSON, but JavaScript line terminators) in upstream responses so clients that treat them as line breaks cannot mis-frame the output; lossless (cf. modelcontextprotocol/typescript-sdk#2155)
- **Argument normalization** — rewrites a `tools/call` request whose `arguments` is `null` to `{}` so strict servers that reject the null form accept the call; on by default, opt out with `--no-normalize-arguments` (cf. modelcontextprotocol/typescript-sdk#2012)
- **Cancellation-aware filtering** — tracks request ids cancelled via `notifications/cancelled` on stdin and drops any late upstream response carrying one of those ids before it reaches the client, per the MCP cancellation spec; on by default (60 s TTL), opt out with `--no-cancel-filter` (cf. anthropics/claude-code#51073)
- **SSE in-flight error synthesis** — on the legacy SSE transport, replies arrive only on the long-lived GET stream; when that stream drops, requests already POSTed would otherwise hang forever. mcp-stdio tracks the ids in flight on the current stream and synthesizes a JSON-RPC `-32000` error for each on a drop — so the client can retry instead of hanging — while auto-reconnecting; cancelled ids are skipped (cf. anthropics/claude-code#60061)
- **Session recovery** — resets MCP session ID on 404 and retries
- **Protocol version header** — captures the negotiated `protocolVersion` from the `initialize` response and injects `MCP-Protocol-Version` on every subsequent Streamable HTTP request (MCP spec rev 2025-06-18); servers that enforce the header would otherwise reject post-initialize requests with `400 Bad Request`
- **Token refresh on 401** — automatically refreshes expired OAuth tokens mid-session (OAuth mode only)
- **Proactive token refresh** — a background timer refreshes the OAuth token shortly before it expires (lead time: `--oauth-refresh-leeway`), so a long-lived session survives gateways that signal token expiry as an HTTP 200 tool-error instead of a transport 401 (e.g. Atlassian's MCP gateway); on by default in OAuth mode, opt out with `--no-proactive-refresh` (#242)
- **Step-up authorization on 403** — on a `Bearer error="insufficient_scope"` challenge, re-authorizes for the union of the granted and required scopes ([RFC 9470](https://www.rfc-editor.org/rfc/rfc9470) / MCP step-up; cf. anthropics/claude-code#44652)
- **Cold-start (`--oauth-eager`)** — answers `initialize` locally and runs the interactive OAuth flow on a background thread, so a 30–180 s browser/SSO/MFA login does not exceed the client's ~60 s initialize timeout. Gated methods return `-32002` until login completes, then `notifications/*/list_changed` tells the client to fetch the now-available lists. Streamable HTTP only; a warm (valid/refreshable) cache is unaffected (#296)
- **Bearer token auth** — via `--bearer-token` flag or `MCP_BEARER_TOKEN` env var
- **Custom headers** — pass any header with `-H` / `--header`
- **Graceful shutdown** — handles SIGTERM/SIGINT
- **Proxy support** — respects `HTTP_PROXY`, `HTTPS_PROXY`, `NO_PROXY` env vars via [httpx](https://www.python-httpx.org/)
- **Minimal dependencies** — only [httpx](https://www.python-httpx.org/); OAuth uses stdlib only
## Install
```bash
pip install mcp-stdio
```
Or with [uv](https://docs.astral.sh/uv/):
```bash
uv tool install mcp-stdio
```
Or run directly without installing:
```bash
uvx mcp-stdio https://your-server.example.com:8080/mcp
```
Or with [Homebrew](https://brew.sh/):
```bash
brew install shigechika/tap/mcp-stdio
```
## Quick Start
```bash
mcp-stdio https://your-server.example.com:8080/mcp
```
With Bearer token authentication:
```bash
# Recommended: use env var (token is hidden from `ps`)
MCP_BEARER_TOKEN=YOUR_TOKEN mcp-stdio https://your-server.example.com:8080/mcp
# Or pass directly (token is visible in `ps` output)
mcp-stdio https://your-server.example.com:8080/mcp --bearer-token YOUR_TOKEN
```
With custom headers:
```bash
mcp-stdio https://your-server.example.com:8080/mcp --header "X-API-Key: YOUR_KEY"
```
With OAuth 2.1 authentication (for servers that require it):
```bash
mcp-stdio --oauth https://your-server.example.com:8080/mcp
# With a pre-registered client ID (skips dynamic registration)
mcp-stdio --oauth --client-id YOUR_CLIENT_ID https://your-server.example.com:8080/mcp
```
With OAuth 2.1 Device Authorization Grant (RFC 8628, for headless/SSH environments):
```bash
mcp-stdio --oauth-device https://your-server.example.com:8080/mcp
```
For legacy MCP servers using the 2024-11-05 SSE transport:
```bash
mcp-stdio --transport sse https://your-server.example.com:8080/sse
```
Check connectivity before use:
```bash
mcp-stdio --check https://your-server.example.com:8080/mcp
# For an SSE server, pass --transport sse so --check runs the legacy
# GET/endpoint/POST handshake instead of a Streamable HTTP probe:
mcp-stdio --check --transport sse https://your-server.example.com:8080/sse
```
## Claude Desktop Configuration
Add to `claude_desktop_config.json`:
```json
{
"mcpServers": {
"my-remote-server": {
"command": "mcp-stdio",
"args": ["https://your-server.example.com:8080/mcp"],
"env": {
"MCP_BEARER_TOKEN": "YOUR_TOKEN"
}
}
}
}
```
Config file locations:
- macOS: `~/Library/Application Support/Claude/claude_desktop_config.json`
- Windows: `%APPDATA%\Claude\claude_desktop_config.json`
- Linux: `~/.config/Claude/claude_desktop_config.json`
## Claude Code Configuration
```bash
claude mcp add my-remote-server \
-e MCP_BEARER_TOKEN=YOUR_TOKEN \
-- mcp-stdio https://your-server.example.com:8080/mcp
```
## Usage
```
mcp-stdio [OPTIONS] URL
Arguments:
URL Remote MCP server URL
Options:
--bearer-token TOKEN Bearer token (or set MCP_BEARER_TOKEN env var)
--oauth Enable OAuth 2.1 authentication (browser flow)
--oauth-device Enable OAuth 2.1 Device Authorization Grant (RFC 8628, headless)
--client-id ID Pre-registered OAuth client ID (or set MCP_OAUTH_CLIENT_ID)
--client-metadata-url URL
HTTPS URL of a Client ID Metadata Document you host
(draft-ietf-oauth-client-id-metadata-document-00), used
as client_id instead of Dynamic Client Registration.
Ignored if --client-id is also given (#60)
--oauth-scope SCOPE OAuth scope to request
--oauth-use-id-token Present the OIDC id_token as the Bearer credential
instead of the access_token (AWS Bedrock AgentCore /
Cognito); falls back to access_token if none is returned (#59)
--oauth-eager Cold-start: answer initialize locally and run the
interactive OAuth flow in the background, so a long
browser/SSO/MFA login does not blow the client's ~60 s
initialize timeout. Streamable HTTP only; ignored on
--transport sse. Warm cache unaffected (#296)
--oauth-refresh-leeway SECONDS
Proactively refresh tokens this many seconds before
expiry (default: 60, or MCP_OAUTH_REFRESH_LEEWAY)
--no-proactive-refresh
Disable the background timer that refreshes the OAuth
token before it expires. On by default in OAuth mode;
keeps long sessions alive against gateways that signal
expiry as an HTTP 200 tool-error rather than a 401 (#242)
--oauth-timeout SECONDS
Seconds to wait for the interactive OAuth flow (browser
callback / device-code confirmation) before giving up
(default: 120; OAuth only)
--no-resource-indicator
Omit the RFC 8707 resource parameter from all OAuth
requests. Required for AS that reject it, such as
Microsoft Entra ID v2 with api:// scopes (AADSTS9010010).
Persisted in the token store so proactive refreshes
and step-up flows stay consistent
--oauth-resource URI Send this exact RFC 8707 resource value on every OAuth
request instead of the server-URL-derived one. Required
for AS that demand a specific resource identifier, e.g.
Microsoft Entra ID's App ID URI api://<app-id>. Persisted
in the token store. Mutually exclusive with
--no-resource-indicator
-H, --header 'Key: Value' Custom header (can be repeated)
--transport {streamable-http,sse}
Transport type (default: streamable-http)
--timeout-connect SEC Connection timeout (default: 10)
--timeout-read SEC Read timeout (default: 120)
--sse-read-timeout SEC Idle read timeout on the SSE GET stream
(default: 300; 0 disables; SSE transport only)
--no-tcp-keepalive Disable TCP keepalive on the HTTP socket
--max-message-size BYTES
Cap on a single upstream response body (JSON or
cumulative SSE stream) buffered before parsing
(default: 10 MiB; 0 disables the cap; #416).
Sends Accept-Encoding: identity by default (#417);
-H 'Accept-Encoding: gzip'/deflate opts back in
with a genuinely size-bounded decoder (#418) —
anything else needs --max-message-size 0.
Also covers this relay's own OAuth traffic (#419)
--no-cancel-filter Disable the cancel-aware response filter (drops late
responses for ids cancelled via notifications/cancelled)
--no-normalize-arguments
Disable rewriting a tools/call request's
arguments:null to {} before forwarding
--check Check connection and exit
-V, --version Show version
-h, --help Show help
```
Run `mcp-stdio --help` for the full per-flag detail (platform notes and issue references are more verbose than this table).
## Reverse gateway: `serve` mode
The default mode bridges **stdio → HTTP** (client side). The `serve` subcommand
is the mirror image — **HTTP → stdio** — exposing a local stdio MCP server as a
Streamable HTTP MCP endpoint so clients that cannot spawn it locally can reach
it over the network:
```mermaid
flowchart BT
A["MCP client<br>Claude Code / Desktop<br>(or mcp-stdio --oauth)"]
B("mcp-stdio serve<br><b>HTTP → stdio</b> gateway<br>auth: none / static token /<br>embedded OAuth 2.1 AS")
C["local stdio<br>MCP server"]
A <== "Streamable HTTP<br>Bearer / OAuth 2.1 (PKCE)" ==> B
B <-- "stdio (spawned child)" --> C
```
This is the mirror of the client-side diagram at the top: there mcp-stdio is
**stdio → HTTP**; here it is **HTTP → stdio**.
```bash
mcp-stdio serve --port 8080 -- python -m my_mcp_server
```
Then point any MCP client (including mcp-stdio itself) at it:
```bash
mcp-stdio --check http://127.0.0.1:8080/mcp
```
- Stdlib only (`http.server`) — adds no runtime dependency.
- Implements the Streamable HTTP request/response and notification semantics,
session management, plus a GET SSE channel for server-initiated messages.
- **Authentication is optional and layered:**
- *No token* — the endpoint is open (run it behind a TLS-terminating proxy).
- *Static token* (`--auth-token` / `MCP_STDIO_SERVE_TOKEN`) — acts as an OAuth
Resource Server: MCP requests require `Authorization: Bearer <token>`, and a
401 advertises [RFC 9728](https://www.rfc-editor.org/rfc/rfc9728) Protected
Resource Metadata at `/.well-known/oauth-protected-resource`.
- *Embedded OAuth AS* (`--enable-oauth`) — a minimal OAuth 2.1 Authorization
Server (PKCE auth-code, [RFC 7591](https://www.rfc-editor.org/rfc/rfc7591)
dynamic client registration with the `invalid_redirect_uri` error per §3.2.2,
refresh, opaque in-memory tokens, stdlib only). An https issuer echoes the
[RFC 9207](https://www.rfc-editor.org/rfc/rfc9207) `iss` parameter on the
authorization response (mix-up defence) and advertises it in metadata.
The mcp-stdio client's `--oauth` flow then works against the gateway.
- Embedded-AS token security: the Resource Server validates token audience
([RFC 8707](https://www.rfc-editor.org/rfc/rfc8707) / MCP — a token issued for
another resource is rejected); a presented-but-invalid token gets
`error="invalid_token"` ([RFC 6750](https://www.rfc-editor.org/rfc/rfc6750)
§3.1); and replaying an authorization code or a rotated refresh token revokes
the whole grant family ([RFC 6749](https://www.rfc-editor.org/rfc/rfc6749)
§4.1.2 / [RFC 9700](https://www.rfc-editor.org/rfc/rfc9700) §4.14.2), with a
brief grace window so a benign client retry is not punished.
- **Multi-client isolation by session** — each MCP session gets its own spawned
backend child, so concurrent clients are isolated by process boundary (a
JSON-RPC id collision across clients can never cross responses). Per the MCP
Streamable HTTP spec, `initialize` mints an `Mcp-Session-Id`, every later
request carries it, an unknown/terminated id gets `404` (the client then
re-initializes), and a `DELETE` tears that session's child down. A
concurrent-session cap guards an open gateway against unbounded child spawns.
When OAuth is enabled each session is **bound to the authenticated user** — a
session id presented with a different user's token is rejected (`404`), so a
leaked id cannot cross tenants.
Static-token example (token via env so it is not visible in `ps`):
```bash
MCP_STDIO_SERVE_TOKEN=your-secret mcp-stdio serve --port 8080 -- python -m my_mcp_server
mcp-stdio --bearer-token your-secret --check http://127.0.0.1:8080/mcp
```
Embedded-OAuth example. User authentication is **delegated to a fronting
reverse proxy** that asserts the logged-in user via a header
(`--trusted-user-header`, only trusted behind a proxy that strips client copies).
`--dev-user` is an **insecure** loopback-only shortcut for local testing:
```bash
mcp-stdio serve --enable-oauth --public-url http://127.0.0.1:8080 \
--dev-user alice --port 8080 -- python -m my_mcp_server
mcp-stdio --oauth http://127.0.0.1:8080/mcp
```
Options: `--host` (default `127.0.0.1`), `--port` (default `8080`), `--path`
(default `/mcp`), `--auth-token TOKEN` (or `MCP_STDIO_SERVE_TOKEN`, preferred);
session limits `--max-sessions N` (default `100`; an `initialize` past the cap
gets `503`), `--session-idle-ttl SECONDS` (evict a session and its child
after this much inactivity so a client that disconnects without `DELETE` does
not pin a slot; `0` = disabled, the default), and `--max-sessions-per-owner N`
(on a new `initialize`, LRU-evict that OAuth user's older sessions down to `N`,
reclaiming ghosts left by a client that reconnects without `DELETE`; `0` =
disabled, the default; static-token and open-gateway sessions are exempt);
`--max-message-size BYTES` (reject a request whose declared `Content-Length`
exceeds this with `413`, before reading any of the body; default 10 MiB,
`0` disables the cap; #416); `--user-env VAR` (inject the authenticated principal into each spawned
child's environment under this name, so a multi-user-aware backend can read
its caller's identity without its own OAuth stack — requires
`--enable-oauth`; the open-gateway and shared static-token principals are
exempt, same as `--max-sessions-per-owner`; refuses a search-path /
dynamic-linker variable name such as `PATH`, `LD_PRELOAD`, or `PYTHONPATH`
that the child's own runtime needs to start); and for the embedded AS:
`--enable-oauth`, `--public-url URL` (pins the issuer; recommended behind a
proxy), `--trusted-user-header HEADER`, `--dev-user USER` (insecure, testing
only), `--access-token-ttl SECONDS`, `--allow-redirect-uri URL` (repeatable;
see below), `--token-store PATH` or `--token-store-firestore COLLECTION/DOCUMENT`
(mutually exclusive, see below). Without either, tokens are in-memory only
and a restart invalidates them (the client re-runs `--oauth`). The backend
command follows the options (an optional `--` separator is supported).
- *Non-loopback remote clients* — DCR only accepts an RFC 8252 loopback
`http://` `redirect_uri` by default, which a browser-based remote MCP
client (a web app with a fixed HTTPS OAuth callback, not a locally-run
CLI/native app) cannot satisfy. `--allow-redirect-uri URL` (repeatable)
trusts one additional `redirect_uri` **byte-for-byte** — no host, prefix,
or port matching — so add only a URL you have verified belongs to a
client you actually trust; each entry is exactly as trusted as a
hardcoded redirect target. It is independent of the loopback path (adding
one never widens the other) and requires `--enable-oauth`.
- *Restart-durable tokens* — `--token-store PATH` persists the issued
tokens, rotation tombstones, and client registrations to a JSON file
(created `0600`, written atomically on every state change), so a client
that held a valid token before a restart keeps calling tools without a
new interactive authorization, and a refresh presented after the restart
is honored. This keeps deploys transparent for remote clients that do not
re-authorize on `401`/`invalid_grant` (they would otherwise replay the
dead token indefinitely and appear connected while their tools silently
vanish). Refresh-token reuse detection and grant-family revocation
survive the restart too — the consumption ledger is part of the persisted
state. The file is credential material: guard it like a private key, and
give each `serve` process its own path — a sidecar `.lock` file refuses a
second process at startup (sharing one store would silently clobber
issued tokens), and the path is probe-written at launch so a
misconfigured target fails the start instead of silently disabling
persistence. Requires `--enable-oauth` (#277).
- *Restart-durable tokens, no local disk* — `--token-store-firestore
COLLECTION/DOCUMENT` persists the same state as `--token-store` (same
JSON-shaped snapshot, same probe-write-at-launch fail-fast behavior) to
one [Firestore](https://cloud.google.com/firestore) document instead of
a local file, for a deployment with no durable local disk (Cloud Run and
similar). The GCP project is resolved the standard google-cloud way
(`GOOGLE_CLOUD_PROJECT` env var, or ADC on Cloud Run) — there is no
separate `--project` flag. Requires the `google-cloud-firestore` package
(`pip install mcp-stdio[firestore]`, an optional extra — plain
`pip install mcp-stdio` never needs it) and `--enable-oauth`. **Unlike
`--token-store` there is no lock against two processes sharing one
document**, but each write goes through a read-merge-write transaction
rather than a blind overwrite (#406), so a brief overlap between two
writers (e.g. a Cloud Run revision cutover) does not silently discard
tokens either side issued or rotated during the overlap. One residual
gap remains: a token revoked (replay detected) or evicted for capacity
during that same overlap window can still be resurrected by a
concurrently-stale writer, since those removals carry no tombstone
(#428). Mutually exclusive with `--token-store`.
- *Path-scoped issuer* — `--public-url` retains a path, so several
`--enable-oauth` backends can share one host behind a reverse proxy, each
under its own prefix (e.g. `--public-url https://gw.example.org/team-a`
serving `https://gw.example.org/team-a/mcp`). The issuer becomes
`https://gw.example.org/team-a`, its AS endpoints live under the prefix
(`/team-a/authorize`, `/token`, `/register`), and the well-known documents
sit at the [RFC 8414](https://www.rfc-editor.org/rfc/rfc8414) §3.1 /
[RFC 9728](https://www.rfc-editor.org/rfc/rfc9728) §3.1 root-inserted
locations (`/.well-known/oauth-authorization-server/team-a`,
`/.well-known/oauth-protected-resource/team-a/mcp`) — byte-symmetric with
the client's path-aware discovery. A bare-origin `--public-url` behaves
exactly as before (#245).
### Multi-user deployment
`serve` is built for multiple concurrent users. Each MCP session gets its own
spawned backend child and — with OAuth enabled — is bound to the authenticated
user, so users are isolated by **process boundary** and a leaked session id
cannot cross tenants.
End-user login is delegated to a fronting reverse proxy that performs the real
SSO and asserts the user via `--trusted-user-header` (trusted ONLY because the
proxy strips any client-supplied copy). The embedded AS then mints per-user
tokens, and the gateway binds each session to that user.
```mermaid
flowchart TD
UA["User A<br>mcp-stdio --oauth"]
UB["User B<br>mcp-stdio --oauth"]
RP["Reverse proxy<br>SSO login, sets X-Forwarded-User<br>strips any client-supplied copy"]
GW["mcp-stdio serve --enable-oauth<br>--trusted-user-header X-Forwarded-User"]
CA["stdio child<br>session of A"]
CB["stdio child<br>session of B"]
UA == "Streamable HTTP<br>OAuth 2.1 (PKCE)" ==> RP
UB == "Streamable HTTP<br>OAuth 2.1 (PKCE)" ==> RP
RP ==> GW
GW -- "spawn per session" --> CA
GW -- "spawn per session" --> CB
```
Gateway (bound to loopback, behind the proxy):
```bash
mcp-stdio serve --enable-oauth \
--public-url https://mcp.example.org \
--trusted-user-header X-Forwarded-User \
--max-sessions 200 --session-idle-ttl 900 --max-sessions-per-owner 1 \
--host 127.0.0.1 --port 8080 -- python -m my_mcp_server
```
- `--public-url` pins the issuer to the external HTTPS URL the proxy serves.
- `--trusted-user-header` is the header the proxy sets after login; the gateway
trusts it only because the proxy strips any client-supplied copy.
- `--max-sessions` caps concurrent per-user children; `--session-idle-ttl`
reclaims a child after a user disconnects without sending `DELETE`.
- `--max-sessions-per-owner` reclaims a user's *previous* sessions the moment
they re-initialize, so a client that reconnects without `DELETE` (common for
hosted connectors) no longer leaves ghosts. Because ghosts are reclaimed at
reconnect rather than only by the idle reaper, a longer `--session-idle-ttl`
no longer risks ghosts filling `--max-sessions` — which lets an interactive
client with pauses avoid frequent re-initialization.
Each user points their client at the gateway, runs the OAuth flow once, and is
served by a dedicated child:
```bash
mcp-stdio --oauth https://mcp.example.org/mcp
```
Notes:
- **Isolation is by process boundary** — user A and user B never share a child,
so per-connection backend state (or a JSON-RPC id collision) cannot leak
across them.
- The backend command is a **template**: every session spawns the same command
as a fresh child. Identity is enforced at the gateway (session→user binding);
it is not injected into the child today, so a backend that needs per-user
context should derive it from the request, or run one gateway per backend
configuration (optionally multiplexed by path — see *Path-scoped issuer*).
## Workarounds
See [WORKAROUNDS.md](WORKAROUNDS.md) for known issues in Claude Code, Claude Desktop, mcp-remote, the MCP SDKs, and Windows that mcp-stdio addresses.
## How It Works
1. If `--oauth` (browser) or `--oauth-device` (headless, RFC 8628) is set, obtains an access token (cached → refresh → browser/device flow)
2. Reads JSON-RPC messages from stdin (sent by Claude Desktop/Code)
3. Relays them over HTTPS to the remote MCP server
4. Parses responses and writes them to stdout
5. On 401 (OAuth mode only), refreshes the access token and retries; with static `--bearer-token` / `-H` auth the 401 is surfaced to the client
6. In OAuth mode a background timer also refreshes the token shortly before it expires (`--oauth-refresh-leeway`), independent of request flow — this keeps long sessions alive against gateways that report token expiry as an HTTP 200 tool-error rather than a 401 (opt out with `--no-proactive-refresh`)
Transport details:
- **Streamable HTTP** (default) — each stdin message is a single POST; session state is tracked via the `Mcp-Session-Id` header and re-initialized automatically on 404. The negotiated `MCP-Protocol-Version` header is sent on every post-initialize request (spec rev 2025-06-18).
- **SSE** (MCP 2024-11-05 legacy) — a persistent `GET` stream delivers responses and the initial `endpoint` event containing the POST URL; the stream auto-reconnects on disconnect.
OAuth tokens are stored in `~/.config/mcp-stdio/tokens.json` (permissions 0600).
## License
MIT