casbin-fastapi-decorator 0.1.3

Casbin authorization decorator factory for FastAPI

casbin-fastapi-decorator

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

Decorators are applied to routes — no middleware or dependencies in the endpoint signature.

Installation

pip install casbin-fastapi-decorator

Additional providers:

pip install "casbin-fastapi-decorator[jwt]"   # JWT authentication
pip install "casbin-fastapi-decorator[db]"    # Policies from DB (SQLAlchemy)

Quick start

import casbin
from fastapi import FastAPI, HTTPException
from casbin_fastapi_decorator import AccessSubject, PermissionGuard

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

async def get_enforcer() -> casbin.Enforcer:
    return casbin.Enforcer("model.conf", "policy.csv")

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

app = FastAPI()

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

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

# 5. Dynamic check — value 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 an exception)
require_permission(*args)	Decorator: permission check via enforcer.enforce(user, *args)

AccessSubject

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

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

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.

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

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

Examples

Example	Description
examples/core	Bearer token auth, file-based Casbin policies
examples/core-jwt	JWT auth via JWTUserProvider, file-based policies
examples/core-db	Bearer token auth, policies from SQLite via DatabaseEnforcerProvider

Development

Requires Python 3.10+, uv, task.

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

Individual package tasks:

task core:lint         # lint core only
task core:test         # test core only
task jwt:lint          # lint JWT package
task jwt:test          # test JWT package
task db:lint           # lint DB package
task db:test           # test DB package (requires Docker for testcontainers)

License

MIT