How do you implement role-based access control (RBAC) using FastAPI dependencies?

FastAPI's dependency injection makes RBAC clean: create a higher-order dependency that checks the current user's role. Inject it into routes that require elevated permissions.

from fastapi import FastAPI, Depends, HTTPException, status
from typing import Annotated
from enum import Enum

app = FastAPI()

class Role(str, Enum):
    user  = "user"
    admin = "admin"

class User:
    def __init__(self, username: str, role: Role):
        self.username = username
        self.role = role

# Simulated auth — in reality decode a JWT
def get_current_user() -> User:
    return User(username="alice", role=Role.user)

# Higher-order dependency factory — creates a role checker
def require_role(role: Role):
    def checker(user: Annotated[User, Depends(get_current_user)]) -> User:
        if user.role != role:
            raise HTTPException(
                status_code=status.HTTP_403_FORBIDDEN,
                detail=f"Requires {role} role",
            )
        return user
    return checker

# Public route — any authenticated user
@app.get("/profile")
def profile(user: Annotated[User, Depends(get_current_user)]):
    return {"username": user.username, "role": user.role}

# Admin-only route
@app.delete("/users/{user_id}")
def delete_user(
    user_id: int,
    _: Annotated[User, Depends(require_role(Role.admin))],
):
    return {"deleted": user_id}

# Router-level dependency — apply to all routes in a router
from fastapi import APIRouter
admin_router = APIRouter(
    prefix="/admin",
    dependencies=[Depends(require_role(Role.admin))],
)

@admin_router.get("/stats")
def admin_stats():
    return {"total_users": 42}

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