15 Authentication Jwt Oauth2

title: JWT and OAuth2 Authentication in FastAPI REST APIs weight: 25 date: 2026-06-28 lastmod: 2026-06-28 description: Implement JWT and OAuth2 authentication in FastAPI using OAuth2PasswordBearer, JWT token generation, password hashing with passlib, and dependency injection. tags: [api-development, fastapi]

FastAPI authentication uses OAuth2PasswordBearer for extracting tokens, PyJWT for signing and verification, passlib for password hashing, and dependency injection for reusable auth checks across all routes.

```python
# app/auth.py
from datetime import datetime, timedelta
from typing import Optional
from jose import JWTError, jwt
from passlib.context import CryptContext
from fastapi import Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer

SECRET_KEY = "your-secret-key-keep-it-secret"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

pwd_context = CryptContext(schemes=["bcrypt"], deprecated="auto")
oauth2_scheme = OAuth2PasswordBearer(tokenUrl="api/auth/login")

def verify_password(plain_password: str, hashed_password: str) -> bool:
    return pwd_context.verify(plain_password, hashed_password)

def get_password_hash(password: str) -> str:
    return pwd_context.hash(password)

def create_access_token(data: dict, expires_delta: Optional[timedelta] = None):
    to_encode = data.copy()
    expire = datetime.utcnow() + (expires_delta or timedelta(minutes=15))
    to_encode.update({"exp": expire})
    return jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)

async def get_current_user(token: str = Depends(oauth2_scheme), db: Session = Depends(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, SECRET_KEY, algorithms=[ALGORITHM])
        user_id: int = payload.get("sub")
        if user_id is None:
            raise credentials_exception
    except JWTError:
        raise credentials_exception

    user = db.query(models.User).filter(models.User.id == user_id).first()
    if user is None:
        raise credentials_exception
    return user

# app/routes/auth.py
@router.post("/auth/login")
def login(form_data: OAuth2PasswordRequestForm = Depends(), db: Session = Depends(get_db)):
    user = db.query(models.User).filter(models.User.email == form_data.username).first()
    if not user or not verify_password(form_data.password, user.password):
        raise HTTPException(status_code=401, detail="Incorrect email or password")
    access_token = create_access_token(data={"sub": str(user.id)})
    return {"access_token": access_token, "token_type": "bearer"}

What's Next

Now learn about authorization in Building REST APIs with FastAPI.