Validate session cookies in Astro

CSRF protection must be implemented when using cookies and forms. This can be easily done by comparing the Origin and Host header.

We recommend creating a middleware to validate requests and store the current user inside locals. You can get the cookie name with Lucia.sessionCookieName and validate the session cookie with Lucia.validateSession(). Make sure to delete the session cookie if it's invalid and create a new session cookie when the expiration gets extended, which is indicated by Session.fresh.

// src/middleware.ts
import { lucia } from "./auth";
import { verifyRequestOrigin } from "lucia";
import { defineMiddleware } from "astro:middleware";

export const onRequest = defineMiddleware(async (context, next) => {
	if (context.request.method !== "GET") {
		const originHeader = request.headers.get("Origin");
		// NOTE: You may need to use `X-Forwarded-Host` instead
		const hostHeader = request.headers.get("Host");
		if (!originHeader || !hostHeader || !verifyRequestOrigin(originHeader, [hostHeader])) {
			return new Response(null, {
				status: 403
			});
		}
	}

	const sessionId = context.cookies.get(lucia.sessionCookieName)?.value ?? null;
	if (!sessionId) {
		context.locals.user = null;
		context.locals.session = null;
		return next();
	}

	const { session, user } = await lucia.validateSession(sessionId);
	if (session && session.fresh) {
		const sessionCookie = lucia.createSessionCookie(session.id);
		context.cookies.set(sessionCookie.name, sessionCookie.value, sessionCookie.attributes);
	}
	if (!session) {
		const sessionCookie = lucia.createBlankSessionCookie();
		context.cookies.set(sessionCookie.name, sessionCookie.value, sessionCookie.attributes);
	}
	context.locals.user = user;
	context.locals.user = session;
	return next();
});

Make sure to type App.Locals as well.

// src/env.d.ts

/// <reference types="astro/client" />
declare namespace App {
	interface Locals {
		user: import("lucia").User | null;
		session: import("lucia").Session | null;
	}
}

This will allow you to access the current user inside .astro pages and API routes.

---
if (!Astro.locals.user) {
    return Astro.redirect("/login")
}
---

import { lucia } from "$lib/server/auth";

export function GET(context: APIContext): Promise<Response> {
	if (!context.locals.user) {
		return new Response(null, {
			status: 401
		});
	}
	// ...
}