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FastAPI-Login

FastAPI-Login tries to provide similar functionality as Flask-Login does.

Installation

$ pip install fastapi-login

Usage

To begin we have to setup our FastAPI app:

from fastapi import FastAPI

SECRET = "your-secret-key"

app = FastAPI()

To obtain a suitable secret key you can run import os; print(os.urandom(24).hex()).

Now we can import and setup the LoginManager, which will handle the process of encoding and decoding our Json Web Tokens.

from fastapi_login import LoginManager
manager = LoginManager(SECRET, tokenUrl='/auth/token')

For the example we will use a dictionary to represent our user database. In your application this could also be a real database like sqlite or Postgres. It does not matter as you have to provide the function which retrieves the user.

fake_db = {'johndoe@e.mail': {'password': 'hunter2'}}

Now we have to provide the LoginManager with a way to load our user. The user_loader callback should either return your user object or None

@manager.user_loader
def load_user(email: str):  # could also be an asynchronous function
    user = fake_db.get(email)
    return user

Now we have to define a way to let the user login in our app. Therefore we will create a new route:

from fastapi import Depends
from fastapi.security import OAuth2PasswordRequestForm
from fastapi_login.exceptions import InvalidCredentialsException

@app.post('/auth/token')
def login(data: OAuth2PasswordRequestForm = Depends()):
    email = data.username
    password = data.password

    user = load_user(email)  # we are using the same function to retrieve the user
    if not user:
        raise InvalidCredentialsException  # you can also use your own HTTPException
    elif password != user['password']:
        raise InvalidCredentialsException

    access_token = manager.create_access_token(
        data=dict(sub=email)
    )
    return {'access_token': access_token, 'token_type': 'bearer'}

Now whenever you want your user to be logged in to use a route, you can simply use your LoginManager instance as a dependency.

# this has to be set first in order to use the instance as dependency
manager.tokenUrl = '/auth/token'


@app.get('/protected')
def protected_route(user: Depends(manager)):
    ...

You can also set the tokenUrl as a argument when initiating LoginManager.

manager = LoginManager(SECRET, App, tokenUrl="route/to/your/login/route")

If you also want to handle a not authenticated error, you can add your own subclass of Exception to the LoginManager.

from starlette.responses import RedirectResponse

class NotAuthenticatedException(Exception):
    pass

# these two argument are mandatory
def exc_handler(request, exc):
    return RedirectResponse(url='/login')

manager.not_authenticated_exception = NotAuthenticatedException
# You also have to add an exception handler to the your app instance
app.add_exception_handler(NotAuthenticatedException, exc_handler)

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