Installing Requirements and Understanding JWTs

Before we dive into implementing user authentication in FastAPI, let’s ensure we have the necessary requirements installed and understand the basics of JSON Web Tokens (JWTs). JWTs are a popular choice for token-based authentication due to their security and ease of use.

Installing Requirements

You’ll need the following libraries:

• FastAPI: The web framework for building APIs
• uvicorn: A ASGI server for running FastAPI applications
• PyJWT: A library for working with JWTs
• Pydantic: A data validation and serialization library

Install these libraries using pip:

Bash

pip install fastapi uvicorn PyJWT pydantic

Understanding JWTs

A JWT is a JSON object that contains three parts, separated by dots:

• Header: Contains metadata about the token, such as the algorithm used to sign it.
• Payload: Contains claims about the user, such as their username and role.
• Signature: A cryptographic signature that ensures the token hasn’t been tampered with.

JWTs can be decoded, verified, and validated using the appropriate cryptographic algorithms.

Creating a JWT

Here’s a basic example of creating a JWT using the PyJWT library:

Python

import jwt

def create_access_token(data: dict):
    token = jwt.encode(data, "your_secret_key", algorithm="HS256")
    return token

Decoding a JWT

To decode a JWT, you need the secret key used to sign it:

Python

def decode_access_token(token: str):
    data = jwt.decode(token, "your_secret_key", algorithms=["HS256"])
    return data

Security Considerations

• Secret Key: Keep your secret key secret and avoid sharing it with anyone.
• Algorithm: Choose a secure algorithm for signing JWTs, such as HS256 or RS256.
• Expiration: Set an expiration time for JWTs to prevent unauthorized access.
• Refresh Tokens: Consider using refresh tokens to allow users to renew their access tokens without re-authenticating.