feat(gnoweb): add secure headers by default & timeout configuration

[gfanton]

This PR adds the following secure headers by default strict=true to gnoweb:

func SecureHeadersMiddleware(next http.Handler, strict bool) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Prevent MIME type sniffing by browsers. This ensures that the browser
		// does not interpret files as a different MIME type than declared.
		w.Header().Set("X-Content-Type-Options", "nosniff")

		// Prevent the page from being embedded in an iframe. This mitigates
		// clickjacking attacks by ensuring the page cannot be loaded in a frame.
		w.Header().Set("X-Frame-Options", "DENY")

		// Control the amount of referrer information sent in the Referer header.
		// 'no-referrer' ensures that no referrer information is sent, which
		// enhances privacy and prevents leakage of sensitive URLs.
		w.Header().Set("Referrer-Policy", "no-referrer")

		// In `strict` mode, prevent cross-site resource forgery and enforce https
		if strict {
			// Define a Content Security Policy (CSP) to restrict the sources of
			// scripts, styles, images, and other resources. This helps prevent
			// cross-site scripting (XSS) and other code injection attacks.
			// - 'self' allows resources from the same origin.
			// - '*' allows images from any external source.
			// - data: is not included to prevent inline images (e.g., base64-encoded images).
			w.Header().Set("Content-Security-Policy", "default-src 'self'; script-src 'self'; style-src 'self'; img-src 'self' *; font-src 'self'")

			// Enforce HTTPS by telling browsers to only access the site over HTTPS
			// for a specified duration (1 year in this case). This also applies to
			// subdomains and allows preloading into the browser's HSTS list.
			w.Header().Set("Strict-Transport-Security", "max-age=31536000; includeSubDomains; preload")
		}

		next.ServeHTTP(w, r)
	})
}

I've also enforced a timeout on read/write/idle (default to 1 minute).

cc @kristovatlas

[Gno2D2]

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[codecov]

Codecov Report

Attention: Patch coverage is 16.98113% with 44 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
gno.land/cmd/gnoweb/main.go	16.98%	43 Missing and 1 partial ⚠️

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[aeddi]

Overall LGTM 👍 I just asked a question bellow about your strict mode

[kristovatlas]

Can a user upload a .js file as part of their realm and use this to bypass CSP projection due to script-src 'self' ?

[kristovatlas]

This is a good resource for security headers:
https://cheatsheetseries.owasp.org/cheatsheets/HTTP_Headers_Cheat_Sheet.html

Notwithstanding my above query, the other headers set look good.

Another header we might want to consider:

Permissions-Policy: geolocation=(), camera=(), microphone=()

Once this is deployed somewhere we should double check headers with https://securityheaders.com/

[alexiscolin]

@gfanton I fixed the inline CSS issue. It should be better now, even if the render should not be as fast as before (If this causes a FOUSVG issue, I will create a dedicated PR 👍)

[thehowl]

good after changes

[gfanton]

just waiting for @sw360cab for last review, then we can merge

[sw360cab]

LGTM 👍

Headers should be automatically forwarded back and forth in case Gnoweb is behind Proxy/Gateway