FastAPI MultiAuth

Composable authentication sources for FastAPI: bring your own validator, combine multiple schemes with MultiAuth, and get correct OpenAPI documentation by construction.

Documentation: https://fastapi-multiauth.d3vyce.fr

Source Code: https://github.com/d3vyce/fastapi-multiauth

fastapi-multiauth is the composable layer between the raw primitives of fastapi.security and opinionated frameworks like fastapi-users or AuthX. You provide the validator; the library handles extraction, scheme combination, and OpenAPI declaration. No database coupling, no user model, no ready-made login routes.

Installation

uv add fastapi-multiauth

Optional extras pull in their dependencies on demand:

uv add "fastapi-multiauth[jwt]"     # JWTValidator (PyJWT)
uv add "fastapi-multiauth[oauth]"   # OAuth 2.0 / OIDC helpers (httpx-oauth)
uv add "fastapi-multiauth[jwt,oauth]"

Quick Start

from fastapi import FastAPI, Security
from fastapi_multiauth import (
    HTTPBearerAuth,
    APIKeyCookieAuth,
    MultiAuth,
    UnauthorizedError,
)


async def validate_token(token: str) -> dict:
    user = await lookup_user_by_token(token)
    if user is None:
        raise UnauthorizedError()
    return user


async def validate_session(value: str) -> dict:
    return await lookup_user_by_session(value)


bearer = HTTPBearerAuth(validate_token, prefix="user_")
session = APIKeyCookieAuth("session", validate_session, secret_key="...")

# Accept either an API token or a web session on the same route.
auth = MultiAuth(bearer, session)

app = FastAPI()


@app.get("/me")
async def me(user=Security(auth)):
    return user

Features

• BYO validator: every source wraps a sync or async callable you provide; the library never touches your user model or database.
• MultiAuth: try several sources in order on a single route (e.g. web session cookie + API bearer token), with all schemes documented in OpenAPI.
• Built-in sources: covering the standard fastapi.security schemes:
  • HTTPBearerAuth: bearer tokens with optional Stripe-style user_/org_ prefixes to route different token types to different validators, plus generate_token() for secure token creation.
  • APIKeyCookieAuth: cookie sessions with optional HMAC-SHA256 signing (via itsdangerous), embedded expiry, key rotation, and optional per-session ids so your app can list and revoke sessions individually.
  • APIKeyHeaderAuth: X-API-Key-style schemes, with APIKeyQueryAuth for legacy clients that can only pass a query parameter.
  • HTTPBasicAuth: validator(username, password) with WWW-Authenticate realm support.
• Token hashing helpers: hash_token/verify_token_hash package the "store the hash, never the token" pattern with constant-time comparison.
• JWT validation (fastapi-multiauth[jwt] extra): JWTValidator for HTTPBearerAuth: HS256 or provider JWKS (Keycloak/Auth0/Entra/Authentik) with TTL caching and rotation-aware kid refresh, aud/iss/exp checks, configurable scope claims, and a claims_to_identity hook.
• Security scopes: Security(auth, scopes=[...]) forwards the declared scopes to validators that accept a scopes parameter.
• Correct HTTP semantics: 401 with WWW-Authenticate challenges (RFC 7235) and 403 via ForbiddenError.
• OAuth 2.0 / OIDC helpers (fastapi-multiauth[oauth] extra): async discovery with TTL caching, HTTPS enforcement, CSRF-protected state encoding, PKCE (S256), and code exchange delegated to httpx-oauth.

Comparison

An honest map of where fastapi-multiauth sits. It is the composable layer between the raw primitives of fastapi.security and opinionated user frameworks. If you want ready-made /register//login routes and a user model, you want a different tool.

When to pick what:

• fastapi.security alone: one scheme, simple validator, no sessions. The primitives are fine, this library just saves you the boilerplate around them.
• fastapi-multiauth: you own the user store and just need request-time auth: bring your own validator, combine several schemes on one route with MultiAuth, validate opaque tokens or JWTs, and get correct OpenAPI for free. No user model, no issued tokens, no database coupling.
• fastapi-users: you want batteries included (user table, password reset, verified-email flow) and accept its user model. Note it is in maintenance mode.
• AuthX: your session model is "login issues a JWT pair, refresh endpoint rotates it". This library validates JWTs but will never issue them.
• Authlib: you are building an OAuth2/OIDC server, or need a full-featured OAuth client beyond the login flow.

FAQ

Can I use it with sync validators?

Yes, every source accepts sync or async callables (including callable class instances) and awaits them correctly.

Why don't my route scopes show in Swagger UI?

The OpenAPI specification only allows scope lists on oauth2/openIdConnect schemes; for http/apiKey schemes the array must be empty. Enforcement happens at runtime regardless; see Usage → Security scopes.

License

This project is licensed under the MIT License.