Authentication

Starlette offers a simple but powerful interface for handling authentication and permissions. Once you've installed AuthenticationMiddleware with an appropriate authentication backend the request.user and request.auth interfaces will be available in your endpoints.

from starlette.applications import Starlette
from starlette.authentication import (
    AuthCredentials, AuthenticationBackend, AuthenticationError, SimpleUser
)
from starlette.middleware import Middleware
from starlette.middleware.authentication import AuthenticationMiddleware
from starlette.responses import PlainTextResponse
from starlette.routing import Route
import base64
import binascii


class BasicAuthBackend(AuthenticationBackend):
    async def authenticate(self, conn):
        if "Authorization" not in conn.headers:
            return

        auth = conn.headers["Authorization"]
        try:
            scheme, credentials = auth.split()
            if scheme.lower() != 'basic':
                return
            decoded = base64.b64decode(credentials).decode("ascii")
        except (ValueError, UnicodeDecodeError, binascii.Error) as exc:
            raise AuthenticationError('Invalid basic auth credentials')

        username, _, password = decoded.partition(":")
        # TODO: You'd want to verify the username and password here.
        return AuthCredentials(["authenticated"]), SimpleUser(username)


async def homepage(request):
    if request.user.is_authenticated:
        return PlainTextResponse('Hello, ' + request.user.display_name)
    return PlainTextResponse('Hello, you')

routes = [
    Route("/", endpoint=homepage)
]

middleware = [
    Middleware(AuthenticationMiddleware, backend=BasicAuthBackend())
]

app = Starlette(routes=routes, middleware=middleware)

Users

Once AuthenticationMiddleware is installed the request.user interface will be available to endpoints or other middleware.

This interface should subclass BaseUser, which provides two properties, as well as whatever other information your user model includes.

• .is_authenticated
• .display_name

Starlette provides two built-in user implementations: UnauthenticatedUser(), and SimpleUser(username).

AuthCredentials

It is important that authentication credentials are treated as separate concept from users. An authentication scheme should be able to restrict or grant particular privileges independently of the user identity.

The AuthCredentials class provides the basic interface that request.auth exposes:

• .scopes

Permissions

Permissions are implemented as an endpoint decorator, that enforces that the incoming request includes the required authentication scopes.

from starlette.authentication import requires


@requires('authenticated')
async def dashboard(request):
    ...

You can include either one or multiple required scopes:

from starlette.authentication import requires


@requires(['authenticated', 'admin'])
async def dashboard(request):
    ...

By default 403 responses will be returned when permissions are not granted. In some cases you might want to customize this, for example to hide information about the URL layout from unauthenticated users.

from starlette.authentication import requires


@requires(['authenticated', 'admin'], status_code=404)
async def dashboard(request):
    ...

Note

The status_code parameter is not supported with WebSockets. The 403 (Forbidden) status code will always be used for those.

Alternatively you might want to redirect unauthenticated users to a different page.

from starlette.authentication import requires


async def homepage(request):
    ...


@requires('authenticated', redirect='homepage')
async def dashboard(request):
    ...

When redirecting users, the page you redirect them to will include URL they originally requested at the next query param:

from starlette.authentication import requires
from starlette.responses import RedirectResponse


@requires('authenticated', redirect='login')
async def admin(request):
    ...


async def login(request):
    if request.method == "POST":
        # Now that the user is authenticated,
        # we can send them to their original request destination
        if request.user.is_authenticated:
            next_url = request.query_params.get("next")
            if next_url:
                return RedirectResponse(next_url)
            return RedirectResponse("/")

For class-based endpoints, you should wrap the decorator around a method on the class.

from starlette.authentication import requires
from starlette.endpoints import HTTPEndpoint


class Dashboard(HTTPEndpoint):
    @requires("authenticated")
    async def get(self, request):
        ...

Custom authentication error responses

You can customise the error response sent when a AuthenticationError is raised by an auth backend:

from starlette.applications import Starlette
from starlette.middleware import Middleware
from starlette.middleware.authentication import AuthenticationMiddleware
from starlette.requests import Request
from starlette.responses import JSONResponse


def on_auth_error(request: Request, exc: Exception):
    return JSONResponse({"error": str(exc)}, status_code=401)

app = Starlette(
    middleware=[
        Middleware(AuthenticationMiddleware, backend=BasicAuthBackend(), on_error=on_auth_error),
    ],
)