fastapi-rbac-authz 0.4.0

Role-based access control with contextual authorization for FastAPI

fastapi-rbac-authz

Role-based access control with contextual authorization for FastAPI.

Installation

pip install fastapi-rbac-authz

Quick Start

from typing import Annotated
from fastapi import Depends, FastAPI
from fastapi_rbac import (
    RBACAuthz, RBACRouter, Global, Contextual, ContextualAuthz
)

# 1. Define your user model
class User:
    def __init__(self, user_id: str, roles: set[str]):
        self.user_id = user_id
        self.roles = roles

# 2. Define your authentication dependencies
# The library only needs roles - you can authenticate however you like
async def get_current_user() -> User:
    # Your authentication logic here
    return User(user_id="user-1", roles={"viewer"})

async def get_current_user_roles() -> set[str]:
    user = await get_current_user()
    return user.roles

# 3. Define role permissions
PERMISSIONS = {
    "admin": {
        Global("report:*"),         # Admin can do anything with reports
    },
    "viewer": {
        Contextual("report:read"),  # Viewer needs context check
    },
}

# 4. Create a context check (for contextual permissions)
# Context classes are responsible for their own authentication via FastAPI DI
class ReportAccessContext(ContextualAuthz):
    def __init__(
        self,
        report_id: int,  # <-- Injected from path parameter
        user: Annotated[User, Depends(get_current_user)],  # Your auth dependency
    ):
        self.user = user
        self.report_id = report_id

    async def has_permissions(self) -> bool:
        # Your logic: check if user can access this specific report
        allowed_reports = {1, 2, 3}  # e.g., query from database
        return self.report_id in allowed_reports

# 5. Create your app and configure RBAC
app = FastAPI()

RBACAuthz(
    app,
    permissions=PERMISSIONS,
    roles_dependency=get_current_user_roles,  # Returns set[str]
    ui_path="/_rbac",  # Optional: mount visualization UI
)

# 6. Create protected routes
router = RBACRouter(permissions={"report:read"}, contexts=[ReportAccessContext])

@router.get("/reports/{report_id}")
async def get_report(report_id: int):
    return {"report_id": report_id}

@router.post("/reports", permissions={"report:create"})  # Override permissions
async def create_report():
    return {"id": "new-report"}

app.include_router(router, prefix="/api")

Note: The library doesn't care how you authenticate - whether via dependency, middleware, JWT decode, or any other method. You just need to provide a dependency that returns the user's roles as set[str]. Context classes are responsible for their own authentication and can use any FastAPI dependency pattern.

Permission Scopes

Permissions can be granted with two scopes:

Global Scope

Global("report:read")

Global permissions bypass context checks entirely. If a user has a global permission, they can access the resource without any additional validation. Use this for admin roles or service accounts that need unrestricted access.

Contextual Scope

Contextual("report:read")

Contextual permissions require context checks to pass. The user must have the permission AND the context check must return True. Use this for regular users who should only access resources they own or are members of.

Example

PERMISSIONS = {
    "admin": {
        Global("report:*"),         # Can access ALL reports, no questions asked
    },
    "user": {
        Contextual("report:read"),  # Can only read reports they have access to
        Contextual("report:create"),
    },
}

Context Checks

Context checks are classes that implement fine-grained authorization logic. They're regular FastAPI dependencies, so you can inject any parameters (path params, query params, request body, database sessions, etc.). Each context class is responsible for its own authentication via FastAPI's dependency injection.

class ReportAccessContext(ContextualAuthz):
    def __init__(
        self,
        report_id: int,  # Injected from path parameter
        user: Annotated[User, Depends(get_current_user)],  # Your auth dependency
        db: Annotated[AsyncSession, Depends(get_db)],  # Database session
    ):
        self.user = user
        self.report_id = report_id
        self.db = db

    async def has_permissions(self) -> bool:
        # Query database to check if user can access this report
        report = await self.db.get(Report, self.report_id)
        return report is not None and report.owner_id == self.user.user_id

Authorization Flow

When a request hits an RBAC-protected endpoint:

1. Role Resolution
   └── roles_dependency runs → User's roles (set[str]) available

2. Permission Check
   └── Does user have ANY grant (global or contextual) for required permission?
       ├── No  → 403 Forbidden
       └── Yes → Continue

3. Scope Evaluation
   └── Is the grant Global?
       ├── Yes → Access granted (skip context checks)
       └── No  → Continue to context checks

4. Context Checks (only for Contextual grants)
   └── Run all context classes via FastAPI DI (each gets its own user via Depends)
       └── Do ALL contexts return True?
           ├── No  → 403 Forbidden
           └── Yes → Access granted

5. Endpoint Handler Executes

Wildcard Permissions

Use wildcards to grant multiple permissions at once:

Grant	Implies
*	Everything
report:*	report:read, report:create, report:delete, etc.
report:metrics:*	report:metrics:view, report:metrics:export, etc.

PERMISSIONS = {
    "admin": {Global("*")},              # Full access to everything
    "reporter": {Global("report:*")},    # Full access to reports only
}

Running the Example

A complete runnable example is included in the examples/ directory:

# Install dependencies
pip install fastapi-rbac-authz uvicorn

# Run the example
uvicorn examples.basic_app:app --reload

Then open your browser:

• http://localhost:8000/docs - OpenAPI docs to test the API
• http://localhost:8000/_rbac - Authorization visualization UI

Test with different users

The example uses X-Token header for authentication:

# As admin (has Global("*") - full access)
curl -H "X-Token: admin-token" http://localhost:8000/reports
curl -H "X-Token: admin-token" http://localhost:8000/reports/1

# As user (has Contextual permissions - can only access own reports)
curl -H "X-Token: user-token" http://localhost:8000/reports/1  # OK (owns report 1)
curl -H "X-Token: user-token" http://localhost:8000/reports/3  # 403 (doesn't own report 3)

# As viewer (has Contextual read - can only read own reports)
curl -H "X-Token: viewer-token" http://localhost:8000/reports/1  # 403 (doesn't own any)

Visualization UI

Mount the built-in visualization UI to explore your authorization schema:

RBACAuthz(
    app,
    # ...
    ui_path="/_rbac",
)

Visit /_rbac to see an interactive graph showing:

• Roles and their permission grants
• Permissions with scope indicators (global/contextual)
• Endpoints and their required permissions
• Context checks and which endpoints use them

Double-click any node to isolate and explore its relationships.

Screenshots

Full authorization graph

Role isolation view - double-click a role to see what it can access

Endpoint isolation view - double-click an endpoint to see who can access it