Secure FastAPI Application with Oauth2 JWT

In this tutorial, we will show you on how to secure FastAPI REST APIs with Oauth2 JWT. To demonstrate this example, we will create the following REST APIs:

1. Create a new user.
2. Log in to obtain an access token.
3. Access the secured APIs using the access token obtained after a successful login.

To store user data, we'll use a MongoDB database.

FastAPI is based on OpenAPI. OpenAPI was previously known as Swagger. Swagger was orginally designed to generate interactive documentation interfaces.

FastAPI provides several tools for implementing security easily without a big amount of effort and code.

FastAPI defines several security schemes. Some are as follows:

• apiKey: This is an application specific key which can come from a header, cookie or a query parameter.
• http: A standard http authentication system that includes the following:
• bearer : A header Authorization value with a token. It is inherited from OAuth2.
• HTTP basic authentication
• HTTP Digest
• Oauth2: Includes all the OAuth2 process of handling security flows:
• The implicit, clientCredentials, and authorizationCode flows are appropriate for creating authentication providers like Google, Facebook, etc.
• The password flow can be used for handling authentication in the same application directly.
• openIdConnect: This provides a way to discover Oauth2 authentication data automatically. The automatic discovery is defined in the OpenID connect specification.

Follow the steps below to complete this tutorial:

1. Start by creating a new project folder:

mkdir project_name

2. Navigate to your newly created project folder:

cd project_name

3. Create a virtual environment inside the project root directory using the following command:
Windows:

py -m venv env

Unix/macOs:

python3 -m venv env

4. Activate the virtual environment using the command:
Windows:

.\env\Scripts\activate

Unix/macOs:

source env/bin/activate

5. Install the following dependencies for FastAPI, Uvicorn, passlib, python-jose[cryptography], python-multipart, mongoengine:

pip install fastapi

pip install "uvicorn[standard]"

pip install passlib

pip install python-jose[cryptography]

pip install python-multipart

pip install mongoengine

6. Create a directory structure for your FastAPI project. A common structure should look like this:

├── project_name
│   │── env
│   ├── routes
│   │     └── api.py
│   ├── src
│   │    ├── __init__.py
│   │    ├── endpoints
│   │    │      ├── __init__.py
│   │    │      ├── product_service.py
│   │    │      └── user_service.py
│   │    │
│   │    └── models
│   │           ├── __init__.py
│   │           └── user.py
│   │            
│   ├── __init__.py
│   ├── main.py

There are folders named models and endpoints inside the src folder. The models folder contains user.py file. Similarly, the endpoints folder contains user_service.py and product_service.py files with API endpoints.

There is a __init__.py file in every directory or subdirectory. This presence of __init__.py files allows importing code from one file into another.

7. Create a model file named user.py in the src/models directory:

from mongoengine import Document, StringField, DateTimeField, IntField, BooleanField
import datetime

class UserModel(Document):
    _id = IntField()
    username = StringField(max_length=250, required=True)
    password = StringField(max_length=250, required=True)
    disabled = BooleanField(default=False)
    created_date = DateTimeField(default=datetime.datetime.utcnow)
    modified_date = DateTimeField(default=datetime.datetime.utcnow)

8. Create a service file named user_service.py in the src/endpoints directory:

from datetime import datetime, timedelta
from fastapi import APIRouter, Depends, HTTPException, status
from pydantic import BaseModel
from typing import Optional
from src.models.user import UserModel
from passlib.context import CryptContext
from fastapi.security import OAuth2PasswordBearer, OAuth2PasswordRequestForm
import json
from jose import jwt, JWTError

router = APIRouter(
    prefix="/users",
    tags=["users"],
    responses={404: {"description": "Not found"}}
)

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

crypt_context = CryptContext(schemes=["sha256_crypt", "md5_crypt"])

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

oauth2_scheme = OAuth2PasswordBearer(tokenUrl="token")

@router.post("/signup")
async def sign_up(newUser: NewUser):
    user = UserModel(username=newUser.username,
                password=get_password_hash(newUser.password))
    user.save()
    return {"message": "Created user successfully!"}

# run the following on terminal to generate a secret key
# openssl rand -hex 32
SECRET_KEY = "3e8a3f31aab886f8793176988f8298c9265f84b8388c9fef93635b08951f379b"
ALGORITHM = "HS256"
ACCESS_TOKEN_EXPIRE_MINUTES = 30

def create_access_token(data: dict, expires_delta: timedelta):
    to_encode = data.copy()
    expire = datetime.utcnow() + expires_delta
    to_encode.update({"exp": expire})
    encoded_jwt = jwt.encode(to_encode, SECRET_KEY, algorithm=ALGORITHM)
    return encoded_jwt


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


def authenticate(username, password):
    try:
        user = get_user(username)
        password_check = verify_password(password, user['password'])
        return password_check
    except UserModel.DoesNotExist:
        return False

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

@router.post("/token" , response_model=Token)
async def login(form_data: OAuth2PasswordRequestForm = Depends()):
    username = form_data.username
    password = form_data.password
    if authenticate(username, password):
        access_token = create_access_token(
            data={"sub": username}, expires_delta=timedelta(minutes=ACCESS_TOKEN_EXPIRE_MINUTES))
        return {"access_token": access_token, "token_type": "bearer"}
    else:
        raise HTTPException(
            status_code=400, detail="Incorrect username or password")


class TokenData(BaseModel):
    username: Optional[str] = None


def get_user(username: str):
    try:
        user = json.loads(UserModel.objects.get(username=username).to_json())
        return user
    except UserModel.DoesNotExist:
        return None


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
        token_data = TokenData(username=username)
    except JWTError:
        raise credentials_exception
    user = get_user(username=token_data.username)
    if user is None:
        raise credentials_exception
    return user

@router.get("/detail")
async def user_detail(current_user: UserModel = Depends(get_current_user)):
    return {"name": "Danny", "email": "danny@tutorialsbuddy.com"}

9. Create another service file named product_service.py in the src/endpoints directory:

from fastapi import APIRouter, Depends
from src.models.user import UserModel
from src.endpoints.user_service import get_current_user

#APIRouter creates path operations for item module
router = APIRouter(
    prefix="/products",
    tags=["Product"],
    responses={404: {"description": "Not found"}},
)

@router.get("/detail")
async def read_item_detail(current_user: UserModel = Depends(get_current_user)):
    return {"products": [{"id": 1}, {"name": "Smart Phone"}]}
    

10. Create a route file named api.py in the routes/ directory:

from fastapi import APIRouter
from src.endpoints import user_service, product_service

router = APIRouter()
router.include_router(user_service.router)
router.include_router(product_service.router)

11. Create a main file named main.py in the project's root directory:

import uvicorn
from fastapi import FastAPI
from src.endpoints import user_service as user
from mongoengine import connect, disconnect


import uvicorn
from fastapi.middleware.cors import CORSMiddleware
from fastapi import FastAPI
from routes.api import router as api_router

app = FastAPI()

# MongoDB connection parameters
db_host = "127.0.0.1"
db_port = "27017"
db_name = "your-database-name"
db_username = "your-username"
db_password = "your-password"

# Connection string
connection_string = f"mongodb://{db_username}:{db_password}@{db_host}:{db_port}/{db_name}"

# Connect to the database
connect(host=connection_string)

origins = ["http://localhost:8005"]

app.add_middleware(
    CORSMiddleware,
    allow_origins=origins,
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

app.include_router(api_router)

if __name__ == '__main__':
    uvicorn.run(app, host='127.0.0.1', port=8005)
    print("running...")

12. Run the application:

python main.py

Run your application and open http://127.0.0.1:8005/docs in your web browser. You will see list of APIs that you can test:

Calling API to create a new user:



Calling login API to retrieve access token:



Calling secured API using access token: