Originally published at turtledev.io Building on our previous tutorial where we created a SvelteKit SPA with a FastAPI backend, let's add authentication to our application. Building a production app? Check out FastSvelte — a production-ready FastAPI + SvelteKit starter with authentication, payments, and more built-in. This tutorial demonstrates a minimal authentication implementation for learning purposes, covering: HTTP-only cookie-based sessions Reactive auth state management with Svelte 5 runes Protected routes with automatic redirects Optimized auth checks with caching Note: This is a tutorial project for learning concepts. For production applications, use solutions like FastSvelte , Auth.js, Lucia, or your backend framework's authentication library.…