Gatsby, a popular JavaScript static site generator, does not natively support features like user authentication, but FusionAuth can effectively integrate this functionality. This blog post guides users through creating a Gatsby site with FusionAuth for secure user login and profile access, employing the OAuth Authorization Code workflow with PKCE extension to enhance security. The process involves setting up FusionAuth, creating a Node proxy application to handle access tokens securely, and developing a Gatsby site with client-only routes for authenticated pages. The tutorial includes detailed steps for setting up routes in a Node app, generating and managing PKCE challenges and verifiers, and creating login and logout functionalities. By the end, users can authenticate securely without exposing sensitive information, and the guide suggests further steps like adding user registration and using higher-order components for content protection.