guest-auth

Not a replacement for real authentication. A static-allowlist invite-token gate for pre-production demos and invite-only previews. Pure-ASGI middleware that plugs into any Starlette / FastAPI app in ~5 lines.

Give a tester a link like https://your-app.example.com/?token=tok_abc123; the middleware validates the token against an allowlist you own, exchanges it for an httpOnly cookie, and attaches an identity (token + human-readable recipient label) to the request via a ContextVar that reaches sync endpoints in the threadpool as well.

It also ships guest-auth-tokens, a small offline CLI that turns a list of names into tokens and shareable invite links — see below.

Extracted from a production app and now used by three: Pitchcraft and JobScout (both private) and Rulebook, which is public and builds a full RBAC layer — capability vocabulary, role bundles, require_capability — on top of this library's identity and claims.

Adopting this in a new app? See docs/integration.md for the dependency-injection pattern, the gotchas (init order, pure-ASGI vs BaseHTTPMiddleware, ContextVar propagation), claims resolution, and the constructor reference.

What this is NOT

Naming a library *-auth invites expectations it doesn't meet. To be explicit:

• No password handling, no MFA, no OAuth / OIDC, no account lifecycle. The credential is an opaque token you generate and hand to a tester.
• No token rotation, expiry, revocation-list, or signed cookies. The cookie is httpOnly + Secure + SameSite=Lax with a 30-day convenience lifetime; revoking access means removing the token from the allowlist and redeploying.
• No rate limiting. Compose one separately (e.g. llm-cost-governor ships an IP rate limiter).
• No policy engine. The identity can carry role / scopes claims (see below), but guest-auth never interprets or enforces them — no capability vocabulary, no role→permission bundles, no require_x decorator. That's authz over the claims and it lives in your app.
• Not audited for adversarial threat models. This is a gate to keep pre-production URLs off the open web and attribute per-tester activity, not a substitute for real identity infrastructure. If you're gating production PII or payment flows, use something else.

The value the library provides — a well-scoped ASGI middleware that publishes a per-request identity ContextVar that reaches sync endpoints — is genuinely useful and hard to get right (the "pure-ASGI vs BaseHTTPMiddleware" trap is subtle). Everything above is deferred, not planned.

Install

pip install guest-auth

Requires Python 3.11+. The only runtime dependency is starlette, which any ASGI host already has.

Quick example

from dataclasses import dataclass, field
from fastapi import FastAPI
from guest_auth import InviteAuthMiddleware, get_current_guest


@dataclass
class Settings:
    demo_mode: bool = True
    invite_tokens: dict = field(
        default_factory=lambda: {"tok_abc123": "Jane Tester"}
    )


settings = Settings()
app = FastAPI()


@app.get("/")
def home():
    guest = get_current_guest()
    return {"welcome": guest.recipient if guest else "anonymous"}


app.add_middleware(
    InviteAuthMiddleware,
    config=settings,
    # Optional — pre-rendered HTML for the 401 / welcome page.
    # Omit to use the built-in "This site is currently invite-only." body.
    welcome_html="<h1>Preview build</h1><p>Ask jane@example.com for a link.</p>",
)

Now:

• GET /?token=tok_abc123 → 302 to /, sets guest_session cookie.
• GET / with the cookie → returns {"welcome": "Jane Tester"}.
• GET / without a cookie → 401 with the welcome page.
• Flip settings.demo_mode = False → gate becomes a complete pass-through with no restart.

Core concepts

GuestAuthConfig (Protocol)

The middleware takes a config object that satisfies:

class GuestAuthConfig(Protocol):
    demo_mode: bool
    invite_tokens: Mapping[str, str]  # token → recipient label

Both attributes are read at request time, so mutating a live config instance (a pydantic BaseSettings, a dataclass, whatever) takes effect on the next request without rebuilding the middleware.

GuestIdentity + get_current_guest()

On a successful cookie match, the middleware sets a request-scoped ContextVar with GuestIdentity(token=..., recipient=..., role=..., scopes=...). Anywhere downstream — sync or async, including code paths in Starlette's threadpool — get_current_guest() returns it or None.

Because the middleware is pure-ASGI (not BaseHTTPMiddleware), the ContextVar survives into the threadpool that runs def (sync) endpoints. See the integration doc for why this matters.

Claims: role and scopes

Optionally, the identity carries authorization claims. guest-auth defines their structure and never their meaning — any string is a role, any strings are scopes:

from guest_auth import GuestClaims

def resolve_claims(token: str) -> GuestClaims:
    return GuestClaims(role="level5", scopes=("rules", "faq"))  # your store

app.add_middleware(
    InviteAuthMiddleware, config=settings, claims_resolver=resolve_claims
)

The resolver may be sync or async; a sync one runs in Starlette's threadpool, so a resolver that reads a bucket doesn't stall the event loop. Caching is the resolver's job.

Two contracts to know: resolution failure is soft (log + empty claims, never a 401), and consequently role=None means unresolved, not unprivileged — map it to your own floor explicitly. Full detail in the integration doc.

PathScopedContextVarMiddleware (bonus)

An adjacent generic that ships in the same package: match a regex against scope["path"], publish an extracted value on a caller-supplied ContextVar for the duration of the request. Same pure-ASGI rationale as the auth middleware. Use for /api/things/{id}/… style path-scoped ContextVars (session IDs, tenant IDs, whatever).

Minting invite tokens

Installing the package also installs guest-auth-tokens, a small offline helper for the chore every app behind this middleware repeats: turn a list of names into tokens and links you can send people. Stdlib only — it adds no dependency.

Write one recipient per line (an inline # adds a private note that stays local):

Alice
Mike        # met at worlds
Bob Smith

Then:

guest-auth-tokens gen --names secrets/guests.txt --out secrets/tokens.json --links secrets/links.md --base-url https://your-app.example.com

That writes a {token: label} JSON — feed it to config.invite_tokens however your app prefers — and a markdown file of shareable invite links.

Re-running is merge-preserving: a name that already has a token keeps it, so links you've already sent never break. A name you remove is reported rather than revoked — its token stays valid until you delete it by hand, because revoking someone's access shouldn't be a side effect of regenerating a file.

Both output files contain working credentials. The tool checks whether they're covered by a .gitignore and warns loudly if not.

Note what this deliberately isn't: there's no live allowlist management, no storage backend, and no cloud dependency. Where your app keeps its allowlist and how it refreshes it stays yours.

Development

git clone https://github.com/ecoop/guest-auth
cd guest-auth
python -m venv .venv && source .venv/bin/activate
pip install -e ".[dev]"
pytest
ruff check src tests

CI runs on Python 3.11 through 3.14 via GitHub Actions.

Versioning

Currently v0.2.1. Semver from v1.0.0 onward; anything before is "shipped but pre-stable API — expect breaking changes."

Contributing

Issues and pull requests welcome. For substantive changes, open an issue first — this library has a deliberately small surface and staying small is a feature.

License

MIT. See LICENSE.

Last updated: 2026-09-08