Everything You Need to Know About FastAPI Security With JWT

In today’s digital landscape, it is very important to secure web APIs. It is crucial to protect sensitive user data and prevent unauthorized access whether you are building a small or a large-scale system. FastAPI is a high-performance web framework for building APIs with Python and it offers excellent tools for building secure APIs. One of the popular methods for securing FastAPI is JSON Web Tokens (JWT). This blog will help you to know how to implement JWT authentication in FastAPI.

JWT (JSON Web Token) authentication is a popular method used to secure web applications, including FastAPI applications. In this blog, we will discuss how to implement JWT authentication in FastAPI.

What is JWT Authentication?

JWT authentication is a stateless authentication method that involves generating a token (JWT) containing user information, which is then sent to the client. The client can use this token to access protected resources on the server. The token is signed using a secret key, and the server can verify the authenticity of the token using this key.

Advantages of JWT Authentication:

JWT has gained significant popularity as a robust authentication mechanism. It offers various advantages and provides enhanced security and an improved user experience.

Here are the advantages of using JWT authentication:

1. Stateless Authentication:

The server does not need to store session data. Instead, it is maintained within the token itself. JWT (JSON Web Tokens) authentication is stateless, meaning the server does not need to store session information.

2. Cross-Domain and Cross-Platform Compatibility:

JWTs can be easily shared across different domains and platforms. The cross-domain and cross-platform compatibility makes it a flexible solution for building distributed systems or APIs.
JWTs can be generated and validated by different systems or services. This decentralized nature allows for easier integration with multiple applications and services, making it suitable for microservices architectures and APIs.

3.Enhanced Security:

JWTs can be digitally signed and encrypted, ensuring the integrity and confidentiality of the token. This helps prevent tampering and unauthorized access to sensitive data.

4. Reduced Database Queries:

Since JWTs are self-contained and carry all the necessary user information within the token, there is no need to query the database or perform additional server-side authentication checks for each request.

Disadvantages of JWT Authentication:

While JWT authentication offers numerous advantages, it’s essential to understand its disadvantages too which are associated with its authentication mechanism.

1. Increased Token Size:

JWT authentication is the larger token size which can impact network bandwidth and storage requirements, particularly in scenarios with a high-frequency token exchange.
JWTs can be larger in size compared to other authentication mechanisms, especially when they contain additional user information or custom claims. This can increase the payload size of each request, impacting network bandwidth.

2. Lack of Token Revocation:

JWTs need to be securely stored on the client side, typically in browser storage or mobile device storage. Managing token storage, expiration, and renewal can add complexity to the client-side implementation.

Implementing JWT Authentication with FastAPI

Here we will discuss the process of implementing JWT authentication with FastAPI to enhance your application’s security.
Let’s start by installing the PyJWT package, which will be used to encode and decode JWT tokens.

Next, let’s create a FastAPI app and add a secret key to the settings. This key will be used to sign and verify JWT tokens.

Creating a Login Endpoint

The first step to implementing JWT authentication is creating a login endpoint where users can provide their credentials and receive a JWT token Here is an example of how to create a simple login endpoint that accepts a username and password and returns a JWT token if the credentials are valid.

Here, we will authenticate the user by checking if the username and password provided in the login form are valid. If the credentials are valid, we will generate a JWT token containing the user’s username in the subfield. The token is then returned to the client.

Protecting Endpoints with JWT Authentication

Now that we have a login endpoint that generates JWT tokens, we can use these tokens to protect our endpoints. We will use the Depends() decorator and a custom jwt_auth function to check for valid JWT tokens on protected endpoints.

Here, we will define a jwt_auth function that checks for a valid JWT token in the Authorization header of the request. If a valid token is found, the function decodes the token and returns the payload (in this case, the user’s username). If the token is invalid or missing, the function raises an HTTPException with a 401-status code. We then use the Depends() decorator.

Implementing JWT Authentication in FastAPI using middleware

1. Create a JWTAuthMiddleware class that will handle the JWT authentication:

The JWTAuthMiddleware class takes two arguments: the app instance and a list of unprotected_routes. The unprotected_routes list should contain the paths to the endpoints that do not require authentication.

2. Use the JWTAuthMiddleware on your FastAPI instance:

Here, we will define an unprotected_routes list containing the paths to the /login endpoint, which will not require authentication. We then create an instance of the JWTAuthMiddleware class and pass it to the app instance and the unprotected_routes list. Finally, we will add the middleware instance to the app using the app.middleware() method.

3. Use the Depends() decorator with the jwt_auth function on the protected routes:

That’s it! You can now protect your routes with JWT authentication, while also providing a way to exclude certain endpoints from requiring authentication.

Conclusion:

JWT authentication offers a robust and flexible approach to secure web applications. FastAPI Security with JWT offers various advantages, including enhanced security, stateless authentication, scalability, cross-platform compatibility, and granular authorization.

JWT authentication in FastAPI strengthens the security of your APIs while providing efficient performance and flexibility. You can build robust and secure applications and protect user data.

By following best practices, understanding the potential risks, and staying informed about advancements in the field, developers can leverage JWT authentication effectively to provide secure and seamless user experiences.

If you continue to encounter issues even after implementing these recommendations, please do not hesitate to contact us. Our dedicated technical team will be more than happy to provide further assistance.

Here are some references that can help you with JWT authentication in FastAPI:

1. The official FastAPI documentation provides a detailed guide on authentication and authorization using JWT.
2. PyJWT library:https://pyjwt.readthedocs.io/
3. FastAPI JWT Auth:https://github.com/IndominusByte/fastapi-jwt-auth