OAuth2 with Password (and Bearer) Tokens

# models.py
from sqlalchemy import Column, Integer, String, Boolean
from sqlalchemy.ext.declarative import declarative_base

Base = declarative_base()

class User(Base):
    __tablename__ = "users"

    id = Column(Integer, primary_key=True, index=True)
    username = Column(String, unique=True, index=True)
    hashed_password = Column(String)
    is_active = Column(Boolean, default=True)

# database.py
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URL = "sqlite:///./test.db"  # Use SQLite for simplicity

engine = create_engine(SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False})
SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)

def get_db():
    db = SessionLocal()
    try:
        yield db
    finally:
        db.close()

# schemas.py
from pydantic import BaseModel

class UserCreate(BaseModel):
    username: str
    password: str

class User(BaseModel):
    id: int
    username: str
    is_active: bool

    class Config:
        orm_mode = True

class Token(BaseModel):
    access_token: str
    token_type: str

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

# utils.py
from passlib.context import CryptContext
from jose import JWTError, jwt
from datetime import datetime, timedelta

SECRET_KEY = "your_secret_key"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")

def verify_password(plain_password, hashed_password):
    return pwd_context.verify(plain_password, hashed_password)

def get_password_hash(password):
    return pwd_context.hash(password)

def create_access_token(data: dict, expires_delta: timedelta | None = None):
    to_encode = data.copy()
    if expires_delta:
        expire = datetime.utcnow() + expires_delta
    else:
        expire = datetime.utcnow() + timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES)
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt

# auth.py
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer
from jose import JWTError, jwt
from sqlalchemy.orm import Session
from datetime import datetime, timedelta

from . import models, schemas, utils, database

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def get_user(db, username: str):
    return db.query(models.User).filter(models.User.username == username).first()

def authenticate_user(db, username: str, password: str):
    user = get_user(db, username)
    if not user:
        return False
    if not utils.verify_password(password, user.hashed_password):
        return False
    return user

def create_access_token(data: dict, expires_delta: timedelta | None = None):
    return utils.create_access_token(data, expires_delta)

async def get_current_user(token: str = Depends(oauth2_scheme), db: Session = Depends(database.get_db)):
    credentials_exception = HTTPException(
        status_code=status.HTTP_401_UNAUTHORIZED,
        detail="Could not validate credentials",
        headers={"WWW-Authenticate": "Bearer"},
    )
    try:
        payload = jwt.decode(token, utils.SECRET_KEY, algorithms=[utils.ALGORITHM])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
        token_data = schemas.TokenData(username=username)
    except JWTError:
        raise credentials_exception
    user = get_user(db, username=token_data.username)
    if user is None:
        raise credentials_exception
    return user

# main.py
from fastapi import FastAPI, Depends, HTTPException, status
from sqlalchemy.orm import Session
from fastapi.security import OAuth2PasswordRequestForm

from . import models, schemas, utils, auth, database

models.Base.metadata.create_all(bind=database.engine)

app = FastAPI()

@app.post("/token", response_model=schemas.Token)
async def login_for_access_token(form_data: OAuth2PasswordRequestForm = Depends(), db: Session = Depends(database.get_db)):
    user = auth.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_expires = timedelta(minutes=utils.ACCESS_TOKEN_EXPIRE_MINUTES)
    access_token = auth.create_access_token(
        data={"sub": user.username}, expires_delta=access_token_expires
    )
    return {"access_token": access_token, "token_type": "bearer"}

@app.post("/users/", response_model=schemas.User)
def create_user(user: schemas.UserCreate, db: Session = Depends(database.get_db)):
    hashed_password = utils.get_password_hash(user.password)
    db_user = models.User(username=user.username, hashed_password=hashed_password)
    db.add(db_user)
    db.commit()
    db.refresh(db_user)
    return db_user

@app.get("/users/me/", response_model=schemas.User)
async def read_users_me(current_user: models.User = Depends(auth.get_current_user)):
    return current_user