Reusable OAuth2 Password Bearer JWT Authentication Dependency in FastAPI

from fastapi import Depends, HTTPException, status
from jose import JWTError, jwt
from sqlalchemy.orm import Session

from .database import get_db
from .models import User
from .schemas import TokenData
from .security import ALGORITHM, SECRET_KEY, oauth2_scheme

credentials_exception = HTTPException(
    status_code=status.HTTP_401_UNAUTHORIZED,
    detail="Could not validate credentials",
    headers={"WWW-Authenticate": "Bearer"},
)


def get_current_user(
    token: str = Depends(oauth2_scheme),
    db: Session = Depends(get_db),
) -> User:
    try:
        payload = jwt.decode(token, SECRET_KEY, algorithms=[ALGORITHM])
        username = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = TokenData(username=username)
    except JWTError:
        raise credentials_exception

    user = db.query(User).filter(User.username == token_data.username).first()
    if user is None:
        raise credentials_exception
    return user


def get_current_active_user(
    current_user: User = Depends(get_current_user),
) -> User:
    if current_user.disabled:
        raise HTTPException(status_code=400, detail="Inactive user")
    return current_user

from fastapi import APIRouter, Depends, HTTPException, status
from fastapi.security import OAuth2PasswordRequestForm
from sqlalchemy.orm import Session

from .database import get_db
from .deps import get_current_active_user
from .models import User
from .schemas import Token, UserPublic
from .security import create_access_token, verify_password

router = APIRouter(tags=["auth"])


def authenticate_user(db: Session, username: str, password: str) -> User | None:
    user = db.query(User).filter(User.username == username).first()
    if not user or not verify_password(password, user.hashed_password):
        return None
    return user


@router.post("/token", response_model=Token)
def login_for_access_token(
    form_data: OAuth2PasswordRequestForm = Depends(),
    db: Session = Depends(get_db),
):
    user = authenticate_user(db, form_data.username, form_data.password)
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Incorrect username or password",
            headers={"WWW-Authenticate": "Bearer"},
        )
    access_token = create_access_token(subject=user.username)
    return Token(access_token=access_token, token_type="bearer")


@router.get("/users/me", response_model=UserPublic)
def read_current_user(current_user: User = Depends(get_current_active_user)):
    return current_user

from pydantic import BaseModel, ConfigDict


class Token(BaseModel):
    access_token: str
    token_type: str = "bearer"


class TokenData(BaseModel):
    username: str | None = None


class UserPublic(BaseModel):
    model_config = ConfigDict(from_attributes=True)

    id: int
    username: str
    disabled: bool = False