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FastAPI-Login

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

Documentation

In-depth documentation can but found at fastapi-login.readthedocs.io Some examples can be found here

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, token_url='/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

# the python-multipart package is required to use the OAuth2PasswordRequestForm
@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.

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

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')

# This will be deprecated in the future
# set your exception when initiating the instance
# manager = LoginManager(..., custom_exception=NotAuthenticatedException)
manager.not_authenticated_exception = NotAuthenticatedException
# You also have to add an exception handler to your app instance
app.add_exception_handler(NotAuthenticatedException, exc_handler)

To change the expiration date of the token use the expires_delta argument of the create_access_token method with a timedelta. The default is set 15 min. Please be aware that setting a long expiry date is not considered a good practice as it would allow an attacker with the token to use your application as long as he wants.

from datetime import timedelta

data = dict(sub=user.email)

# expires after 15 min
token = manager.create_access_token(
    data=data
)
# expires after 12 hours
long_token = manager.create_access_token(
    data=data, expires=timedelta(hours=12)
)

Usage with cookies

Instead of checking the header for the token. fastapi-login also support access using cookies.

from fastapi_login import LoginManager

manager = LoginManager(SECRET, token_url='/auth/token', use_cookie=True)

Now the manager will check the requests cookies the headers for the access token. The name of the cookie can be set using manager.cookie_name. If you only want to check the requests cookies you can turn the headers off using the use_header argument

For convenience the LoginManager also includes the set_cookie method which sets the cookie to your response, with the recommended HTTPOnly flag and the manager.cookie_name as the key.

from fastapi import Depends
from starlette.responses import Response


@app.get('/auth')
def auth(response: Response, user=Depends(manager)):
    token = manager.create_access_token(
        data=dict(sub=user.email)
    )
    manager.set_cookie(response, token)
    return response
    

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