JSON Web Tokens (JWTs) have become a popular way to manage authentication and authorization in modern serverless architectures. JWTs allow for secure and stateless authentication by including a digitally signed token in each request. In this blog post, we will explore how to effectively use JWTs in a serverless architecture.

What is JWT?

JWT is an open standard for secure transmission of JSON objects between parties. It consists of three parts: a header, a payload, and a signature. The header identifies the algorithm used for signature generation, while the payload contains the claims or information about the user. The signature ensures that the token is not tampered with.

Generating JWTs

When a user logs in to your application, the server generates a JWT for them. The JWT is then sent to the client, usually stored in a secure cookie or local storage. The client includes the JWT in the Authorization header of subsequent requests to authenticate themselves with the server.

Authenticating JWTs

In a serverless architecture, authentication of JWTs is typically performed at the API Gateway level. The JWT is intercepted before reaching the underlying lambda function, allowing for authentication and authorization checks to be performed without having to modify each function individually.

To authenticate the JWT, the API Gateway verifies the token’s signature using the server’s public key. It then extracts the payload and checks if it contains the necessary claims to authorize the request. If the JWT is valid, the request proceeds to the corresponding lambda function. Otherwise, an authentication error is returned.

Managing Authorization

JWTs are also useful for managing authorization within a serverless architecture. The payload of the JWT can include custom claims that define the user’s roles, permissions, or access levels. These claims can be used to implement fine-grained authorization checks at the API Gateway or within the lambda functions themselves.

For example, you could include a “roles” claim in the JWT payload, specifying whether the user is an admin or a regular user. The lambda functions can then check this claim to ensure that only authenticated admins can perform certain actions.

Revoking JWTs

One challenge of using JWTs in a serverless architecture is token revocation. Since JWTs are stateless, there is no built-in mechanism to revoke a token once it has been issued. This means that if a user’s JWT is compromised or the user’s roles change, they would still have access until the token expires.

To mitigate this issue, you can implement token revocation by maintaining a blacklist of revoked tokens. Each time a token is issued, its unique identifier is stored in a database or cache. When a request with a revoked token is received, the API Gateway can check the blacklist before allowing access.

Conclusion

Using JWTs in a serverless architecture provides a secure and scalable way to handle authentication and authorization. By offloading the authentication logic to the API Gateway, you can ensure that every request is properly authenticated before reaching your lambda functions. Additionally, JWTs allow for flexible authorization checks based on custom claims in the token’s payload.