website/routes/_middleware.ts

import { FreshContext } from '$fresh/server.ts'
import { useCsp } from ':src/csp/middleware.ts'
import { SessionStore } from ':src/session/mod.ts'
import { useSession } from ':src/session/middleware.ts'

export async function handler(request: Request, ctx: FreshContext) {
	// Update fresh context state with session
	ctx.state = { ...ctx.state, session: SessionStore.getFromRequest(request) }

	// Get response
	const response = await ctx.next()

	//Add security headers
	// See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/TLS#http_strict_transport_security
	response.headers.set('Strict-Transport-Security', 'max-age=63072000; includeSubDomains; preload')
	response.headers.set('Content-Security-Policy', "frame-ancestors 'none'; upgrade-insecure-requests")
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/Referrer_policy
	response.headers.set('Referrer-Policy', 'no-referrer, strict-origin-when-cross-origin')
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/MIME_types
	response.headers.set('X-Content-Type-Options', 'nosniff')
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/Clickjacking
	response.headers.set('X-Frame-Options', 'DENY')
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/CORP
	response.headers.set('Cross-Origin-Resource-Policy', 'same-origin')
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity
	//? SRI plugin for non local resources only ?
	//See https://developer.mozilla.org/en-US/docs/Web/Security/Practical_implementation_guides/CSP
	//? fresh useCSP https://fresh.deno.dev/docs/examples/using-csp

	await useCsp(request, response, ctx)
	useSession(request, response, ctx)

	// Allow service worker to serve root scope
	if (ctx.url.pathname.endsWith('island-startserviceworker.js')) {
		response.headers.set('Service-Worker-Allowed', '/')
	}

	return response
}