Part 4: Security and Authentication in FastAPI
Tags: python, fastapi, api, webdev
Published: 2024-05-06 14:23:58

# Part 4: Security and Authentication in FastAPI

In this part of our FastAPI series, we delve into implementing robust security measures to protect your API endpoints. We'll cover basic authentication schemes, token-based authentication using OAuth2, and setting up role-based access control (RBAC).

## **Why Focus on Security?**

Security is paramount for any application that interacts with user data or interfaces with other systems. A secure API guards against unauthorized access and ensures that user data is handled safely. FastAPI provides several tools to help secure your API effectively.

## **OAuth2 with Password and Bearer Tokens**

One of the most common and secure ways to handle authentication in APIs is through OAuth2 with Password (and hashing), which involves token-based credentials.

### **Setting Up Authentication**

First, let's set up the authentication scheme in FastAPI. We'll use OAuth2 with password flow, which is well-suited for securing web and mobile applications.

```python
from fastapi import FastAPI, Depends, HTTPException, status
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
from pydantic import BaseModel

app = FastAPI()

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

def fake_hash_password(password: str):
    return "fakehashed" + password

class User(BaseModel):
    username: str
    email: Optional[str] = None
    full_name: Optional[str] = None
    disabled: Optional[bool] = None

class UserInDB(User):
    hashed_password: str

# Assuming we have a way to fetch user details
def get_user(db, username: str):
    if username == "johndoe":
        return UserInDB(username="johndoe", hashed_password=fake_hash_password("secret"))
    return None

# Authentication function
def authenticate_user(fake_db, username: str, password: str):
    user = get_user(fake_db, username)
    if not user or user.hashed_password != fake_hash_password(password):
        return False
    return user
```

### **Creating a Token Endpoint**

The token endpoint is where users will authenticate using their credentials to receive a token they can use for subsequent requests.

```python
from fastapi import Security
from fastapi.security import OAuth2PasswordRequestForm
from jose import jwt, JWTError

SECRET_KEY = "a_very_secret_key"
ALGORITHM = "HS256"

@app.post("/token")
async def login(form_data: OAuth2PasswordRequestForm = Depends()):
    user = authenticate_user(fake_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 = jwt.encode({"sub": user.username}, SECRET_KEY, algorithm=ALGORITHM)
    return {"access_token": access_token, "token_type": "bearer"}
```

## **Role-Based Access Control (RBAC)**

Role-based access control is a method to provide access based on the user role at an organization level. Let's implement a simple RBAC in FastAPI.

```python
from fastapi import APIRouter, Depends, HTTPException

router = APIRouter()

async def get_current_user(token: str = Depends(oauth2_scheme)):
    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])
        username: str = payload.get("sub")
        if username is None:
            raise credentials_exception
    except JWTError:
        raise credentials_exception
    user = get_user(fake_db, username=username)
    if user is None:
        raise credentials_exception
    return user

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

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

## **Conclusion**

Implementing robust authentication and role-based access control is crucial for securing a FastAPI application. By following these examples, you can set up a secure API that uses OAuth2 for authentication and implements simple RBAC to manage user access based on roles.

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Stay tuned for more advanced topics in this series, where we’ll explore testing strategies, integrate

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