Password hash

By default, FastAPI Users will use the BCrypt algorithm to hash and salt passwords before storing them in the database.

The implementation is provided by Passlib, a battle-tested Python library for password hashing.

Customize CryptContext

If you need to support other hashing algorithms, you can customize the CryptContext object of Passlib.

For this, you'll need to instantiate the PasswordHelper class and pass it your CryptContext. The example below shows you how you can create a CryptContext to add support for the Argon2 algorithm while deprecating BCrypt.

from fastapi_users.password import PasswordHelper
from passlib.context import CryptContext

context = CryptContext(schemes=["argon2", "bcrypt"], deprecated="auto")
password_helper = PasswordHelper(context)

Finally, pass the password_helper variable while instantiating your UserManager:

async def get_user_manager(user_db=Depends(get_user_db)):
    yield UserManager(user_db, password_helper)

Password hashes are automatically upgraded

FastAPI Users takes care of upgrading the password hash to a more recent algorithm when needed.

Typically, when a user logs in, we'll check if the password hash algorithm is deprecated.

If it is, we take the opportunity of having the password in plain-text at hand (since the user just logged in!) to hash it with a better algorithm and update it in database.

Dependencies for alternative algorithms are not included by default

FastAPI Users won't install required dependencies to make other algorithms like Argon2 work. It's up to you to install them.

Full customization

If you don't wist to use Passlib at all – which we don't recommend unless you're absolutely sure of what you're doing — you can implement your own PasswordHelper class as long as it implements the PasswordHelperProtocol and its methods.

from typing import Tuple

from fastapi_users.password import PasswordHelperProtocol

class PasswordHelper(PasswordHelperProtocol):
    def verify_and_update(
        self, plain_password: str, hashed_password: str
    ) -> Tuple[bool, str]:
        ...

    def hash(self, password: str) -> str:
        ...

    def generate(self) -> str:
        ...