casbin-fastapi-decorator 1.2.0

Decorator-based authorization for FastAPI with Casbin, without middleware

casbin-fastapi-decorator

Authorization decorator factory for FastAPI based on Casbin and fastapi-decorators.

📚 Documentation · PyPI · Casbin Ecosystem

---

Decorators are applied directly to routes — no middleware, no extra parameters in your function signatures.

Why decorator, not middleware?

Feature	casbin-fastapi-decorator	fastapi-authz / fastapi-casbin-auth
Approach	Decorator per route	Global middleware
Per-route permission config	✅	❌
Dynamic objects from request	✅ AccessSubject	❌
No extra params in endpoint signature	✅	❌
Native FastAPI DI integration	✅	⚠️ partial
JWT extras	✅	❌
DB-backed policies (SQLAlchemy async)	✅	❌
File policies with hot-reload	✅	❌
Casdoor OAuth2 integration	✅	❌
Works with APIRouter	✅	✅

Middleware-based authorization checks every incoming request globally. With a decorator, you configure permissions exactly where the route is defined — no hidden side effects, no boilerplate dependencies in every function signature.

Installation

pip install casbin-fastapi-decorator

Optional extras — install only what you need:

pip install "casbin-fastapi-decorator[file]"     # File policies with hot-reload (recommended)
pip install "casbin-fastapi-decorator[jwt]"      # JWT authentication
pip install "casbin-fastapi-decorator[db]"       # Policies from DB (SQLAlchemy) with hot-reload
pip install "casbin-fastapi-decorator[casdoor]"  # Casdoor OAuth2

Quick start

from contextlib import asynccontextmanager
from fastapi import FastAPI, HTTPException
from casbin_fastapi_decorator import AccessSubject, PermissionGuard
from casbin_fastapi_decorator_file import CachedFileEnforcerProvider

# 1. Providers — regular FastAPI dependencies
async def get_current_user() -> dict:
    return {"sub": "alice", "role": "admin"}

# CachedFileEnforcerProvider loads the enforcer once and hot-reloads
# automatically when model.conf or policy.csv changes on disk.
enforcer_provider = CachedFileEnforcerProvider(
    model_path="model.conf",
    policy_path="policy.csv",
)

# 2. Decorator factory
guard = PermissionGuard(
    user_provider=get_current_user,
    enforcer_provider=enforcer_provider,
    error_factory=lambda user, *rv: HTTPException(403, "Forbidden"),
)

# 3. Wire lifespan to start/stop the file watcher
@asynccontextmanager
async def lifespan(app: FastAPI):
    async with enforcer_provider:
        yield

app = FastAPI(lifespan=lifespan)

# 4. Authentication only
@app.get("/me")
@guard.auth_required()
async def me():
    return {"ok": True}

# 5. Static permission check
@app.get("/articles")
@guard.require_permission("articles", "read")
async def list_articles():
    return []

# 6. Dynamic check — object resolved from request
async def get_article(article_id: int) -> dict:
    return {"id": article_id, "owner": "alice"}

@app.get("/articles/{article_id}")
@guard.require_permission(
    AccessSubject(val=get_article, selector=lambda a: a["owner"]),
    "read",
)
async def read_article(article_id: int):
    return {"article_id": article_id}

Arguments of require_permission are passed to enforcer.enforce(user, *args) in the same order. AccessSubject is resolved via FastAPI DI, then transformed by the selector.

API

PermissionGuard

PermissionGuard(
    user_provider=...,       # FastAPI dependency that returns the current user
    enforcer_provider=...,   # FastAPI dependency that returns a casbin.Enforcer
    error_factory=...,       # callable(user, *rvals) -> Exception
)

Method	Description
auth_required()	Decorator: authentication only (user_provider must not raise)
require_permission(*args, error_factory=None)	Decorator: permission check via enforcer.enforce(user, *args). Optional error_factory overrides the guard-level factory for this route only.

AccessSubject

AccessSubject(
    val=get_item,                        # FastAPI dependency
    selector=lambda item: item["name"],  # transformation before enforce
)

Wraps a dependency whose value is resolved from the request and passed to the enforcer. By default, selector is identity (lambda x: x).

Per-route error responses

Override the guard-level error_factory on specific routes to customize error handling:

def article_not_found_error(user, *resolved_args) -> HTTPException:
    """Return 404 instead of 403 for denied access."""
    return HTTPException(status_code=404, detail="Article not found")

@app.get("/articles/draft")
@guard.require_permission(
    "article", "write",
    error_factory=article_not_found_error,
)
async def read_draft():
    return {"title": "Draft Article"}

When a user without write permission accesses this route, they'll receive a 404 Not Found instead of the default 403 Forbidden, effectively hiding the resource's existence.

File provider

casbin-fastapi-decorator-file — loads the Casbin enforcer once from model.conf + policy.csv and hot-reloads automatically when either file changes on disk (via watchdog).

pip install "casbin-fastapi-decorator[file]"

from casbin_fastapi_decorator_file import CachedFileEnforcerProvider

enforcer_provider = CachedFileEnforcerProvider(
    model_path="casbin/model.conf",
    policy_path="casbin/policy.csv",
)

@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    async with enforcer_provider:   # starts watchdog
        yield                       # stops watchdog on shutdown

guard = PermissionGuard(
    user_provider=get_current_user,
    enforcer_provider=enforcer_provider,
    error_factory=lambda *_: HTTPException(403, "Forbidden"),
)

Edit policy.csv while the app is running — the enforcer reloads on the next request with zero downtime. The same applies to model.conf changes.

Recommended for all file-based setups. Compared to a plain async def get_enforcer() that returns casbin.Enforcer(...), this provider avoids re-reading files on every request.

See packages/casbin-fastapi-decorator-file/README.md for full API and usage.

JWT provider

casbin-fastapi-decorator-jwt — extracts and validates a JWT from the Bearer header and/or a cookie.

pip install "casbin-fastapi-decorator[jwt]"

See packages/casbin-fastapi-decorator-jwt/README.md for full API and usage.

DB provider

casbin-fastapi-decorator-db — loads Casbin policies from a SQLAlchemy async session with caching and hot-reload.

pip install "casbin-fastapi-decorator[db]"

The enforcer is cached and reloaded automatically when:

• model.conf changes on disk (watchdog)
• DB policy rows change — detected by SHA-256 hash, polled every poll_interval seconds (default 30 s)

from casbin_fastapi_decorator_db import DatabaseEnforcerProvider

enforcer_provider = DatabaseEnforcerProvider(
    model_path="casbin/model.conf",
    session_factory=async_session,
    policy_model=Policy,
    policy_mapper=lambda p: (p.sub, p.obj, p.act),
    poll_interval=30.0,  # seconds between DB hash checks
)

@asynccontextmanager
async def lifespan(app: FastAPI) -> AsyncGenerator[None, None]:
    async with enforcer_provider:   # starts watchdog + polling task
        yield

See packages/casbin-fastapi-decorator-db/README.md for full API and usage.

Casdoor provider

casbin-fastapi-decorator-casdoor — Casdoor OAuth2 authentication and remote Casbin policy enforcement.

pip install "casbin-fastapi-decorator[casdoor]"

from casbin_fastapi_decorator_casdoor import CasdoorEnforceTarget, CasdoorIntegration

casdoor = CasdoorIntegration(
    endpoint="http://localhost:8000",
    client_id="...", client_secret="...", certificate=cert,
    org_name="my_org", application_name="my_app",
    target=CasdoorEnforceTarget(
        enforce_id=lambda parsed: f"{parsed['owner']}/my_enforcer",
    ),
)
app.include_router(casdoor.router)   # GET /callback, POST /logout
guard = casdoor.create_guard()

CasdoorEnforceTarget selects the Casdoor enforce mode — by enforcer, permission, model, resource, or owner. Values can be static strings or callables resolved from the JWT payload at request time.

See packages/casbin-fastapi-decorator-casdoor/README.md for full API, compose pattern, and usage.

Examples

Example	Description
examples/core	Bearer token auth, plain file-based policies
examples/core-file	Bearer token auth, file policies with hot-reload via CachedFileEnforcerProvider
examples/core-jwt	JWT auth via JWTUserProvider, file-based policies
examples/core-db	Bearer token auth, DB policies with hot-reload via DatabaseEnforcerProvider
examples/core-casdoor	Casdoor OAuth2 auth + remote enforcement, facade and compose patterns

Development

Requires Python 3.10+, uv, task.

task install           # uv sync --all-groups + install all packages
task lint              # ruff + ty + bandit for all packages
task tests             # all tests (core + jwt + db + casdoor + file)

Individual package tasks:

task core:lint         task core:test
task jwt:lint          task jwt:test
task db:lint           task db:test         # requires Docker (testcontainers)
task casdoor:lint      task casdoor:test
task file:lint         task file:test

License

MIT