origo 0.1.6

Drop-in OAuth 2.1 provider for servers. Developed originally for custom/private MCP servers. Works with FastMCP, FastAPI, and the raw MCP SDK.

origo

Implements the OAuth2.1 + PKCE flow as a drop-in Starlette based middleware layer, with public and private registration modes.

Drop-in OAuth 2.1 provider, originally developed for use in custom/private MCP servers. Handles the full Authorization Code + PKCE flow with no external identity provider required.

Works with FastMCP, FastAPI, and the raw MCP SDK.

Install

pip install origo

Quickstart

FastMCP

from fastmcp import FastMCP
from origo import OAuthProvider, OAuthMiddleware
from starlette.routing import Mount
from starlette.applications import Starlette
import os

auth = OAuthProvider(
    base_url="https://mcp.yourdomain.com",
    clients={os.getenv("MCP_CLIENT_ID"): os.getenv("MCP_CLIENT_SECRET")},
)

mcp = FastMCP("my-server")

# ... define tools ...

mcp_app = mcp.streamable_http_app()
mcp_app.add_middleware(OAuthMiddleware, provider=auth)

# OAuth must be at root so /.well-known/ discovery works for MCP clients
root = Starlette(routes=[
    Mount("/mcp", app=mcp_app),      # protected MCP endpoint
    Mount("/", app=auth.asgi_app()), # /.well-known/, /authorize, /token, /register
])

FastAPI

from fastapi import FastAPI
from origo import OAuthProvider, OAuthMiddleware
from starlette.routing import Mount
from starlette.applications import Starlette
import os

auth = OAuthProvider(
    base_url="https://api.yourdomain.com",
    clients={os.getenv("OAUTH_CLIENT_ID"): os.getenv("OAUTH_CLIENT_SECRET")},
)

api = FastAPI()
api.add_middleware(OAuthMiddleware, provider=auth)

# ... define routes on api ...

app = Starlette(routes=[
    Mount("/api", app=api),          # protected API routes
    Mount("/", app=auth.asgi_app()), # OAuth at root
])

How this differs from enterprise OAuth

Traditional OAuth deployments separate the authorization server from the resource server — the MCP server asks a dedicated auth service "is this token valid?" on every request (RFC 7662 token introspection). This is correct for multi-tenant systems where tokens need to be revoked instantly across many services.

origo collapses this into a single process. Token validation is an in-memory lookup. Fast, zero network overhead, no second service to run. The tradeoff is that token revocation requires a server restart, and there's no centralized auth service to share across multiple resource servers. This also introduce a single point of failure and security relies on the shared memory with the application it is authenticating for.

Use this when:

• You're running a personal or private server (ex. MCP server) with simple OAuth requirements
• You control who gets client credentials
• Operational simplicity matters more than enterprise auth guarantees

Use a proper auth server (Keycloak, Auth0, etc.) when:

• Multiple users need independent identities
• You need instant token revocation
• You're sharing one auth service across many servers (ex. MCP servers)
• Compliance requirements mandate it

Two Modes

Private (default)

Only pre-registered clients can authenticate. Pass a clients dict:

auth = OAuthProvider(
    base_url="https://mcp.yourdomain.com",
    clients={"my-client-id": "my-client-secret"},
    public_registration=False,  # default
)

Public

Anyone can register as a client dynamically (DCR). A consent page is shown before access is granted:

auth = OAuthProvider(
    base_url="https://mcp.yourdomain.com",
    public_registration=True,
)

Dynamically registered clients must supply redirect_uris at registration time. The /authorize endpoint validates the redirect_uri parameter against that registered list and rejects any URI not on it. Pre-registered clients (supplied via clients=) have no such restriction — any redirect URI is accepted, since the operator controls both sides.

Options

Parameter	Type	Default	Description
base_url	str	required	Public base URL, no trailing slash
clients	dict	None	Pre-registered {client_id: client_secret}
public_registration	bool	False	Allow dynamic client registration
auto_approve	bool	False	Skip consent page, auto-approve all valid clients
token_ttl	int	3600	Access token lifetime in seconds
mcp_path	str	"/mcp"	Path where MCP endpoint is mounted

OAuth Endpoints

Endpoint	Description
GET /.well-known/oauth-authorization-server	Discovery
GET /.well-known/oauth-protected-resource	Resource metadata
POST /register	Dynamic client registration (public mode only)
GET /authorize	Show consent page (or redirect immediately if auto_approve=True)
POST /authorize	Submit consent form
POST /token	Token exchange