Start mode: generated entries render without the CSP nonce, and there is no per-request seam to supply one #388

Problem

A strict CSP (script-src 'nonce-…' 'strict-dynamic', no 'unsafe-inline') cannot be served with Start mode's generated entries. The only nonce input is handleRequest(request, { nonce }), added in #311, and it only reaches two tags: the injected client-entry <script> and the post-flush redirect fallback.

The generated entry renders with a fixed { manifest } and ignores the context it receives:

So even when a host passes nonce, renderToStream never gets it. The hydration bootstrap (_$HY), the streamed data and swap scripts and the modulepreload links all go out without a nonce, and the page does not hydrate under the policy.

There is also no way to supply the nonce from inside the app:

• Deployments that dispatch through the default Fetchable (Nitro calls mod.fetch(req)) never pass options. That is intentional, since the second argument of a Fetchable belongs to the host:

  solid-vite-plugin/src/ssr/index.ts

  Line 1461 in e4cdee4

  ` return handleRequest(request);`,

• start.middleware is the natural place to generate the nonce and set the Content-Security-Policy header, but it only sees (request, next). The options bag is fixed before the chain runs.
• start.setup returns a component and start.renderMode returns a mode, so neither can change the stream options.
• @solidjs/web only reads the nonce from the renderToStream options, not from the request event or locals.

Today the workaround is hand-written entry-server / entry-client files that pass nonce to renderToStream. Entries come in pairs, so both have to be written, and authored entries also give up the generated DefaultErrorBoundary. SolidStart had a per-request seam for this (createHandler(fn, (event) => ({ nonce })), see solidjs/solid-start#2252). #311 ported the client-entry part of that change.

A related bug: the object form CSPNonce that @solidjs/web accepts ({ script, style }) throws in the client-entry transform, because it escapes the value as a string:

TypeError: value.replace is not a function

Reproduction

With @solidjs/vite-plugin 3.0.0-next.47 and @solidjs/web 2.0.0-rc.13, in examples/start-ssr:

const html = await (await handleRequest(new Request('http://localhost/'), { nonce: 'abc' })).text();
// only the client-entry <script> carries nonce="abc";
// the _$HY bootstrap, the data scripts and the modulepreload links do not

await handleRequest(new Request('http://localhost/'), { nonce: { script: 'abc', style: false } });
// TypeError: value.replace is not a function

Proposal

A start.nonce option that follows the renderMode module convention. The option names a module that default-exports (event) => CSPNonce | undefined | Promise<…>. The handler resolves it after the middleware chain, next to resolveRenderMode, so a middleware can generate the nonce, set the header and store it on event.locals:

solid({ start: { middleware: './src/middleware.ts', nonce: './src/nonce.ts' }, ssr: true });

// src/nonce.ts
export default (event: RequestEvent) => event.locals.nonce as string | undefined;

The resolved value (or handleRequest's nonce, which keeps precedence) would go to:

• the generated entry's renderToStream;
• the client-entry tag and createSSRResponse, both through scriptNonce, which also fixes the object form;
• in dev, the head tags the handler injects (the style patch and Vite client scripts, the collected styles, and a csp-nonce meta for the styles the Vite client injects);
• authored entries, as context.nonce.

I have a PR ready and will link it here.