[feature] proof of work scraper deterrence (#4043)

This adds a proof-of-work based scraper deterrence to GoToSocial's middleware stack on profile and status web pages. Heavily inspired by https://github.com/TecharoHQ/anubis, but massively stripped back for our own usecase.

Todo:
- ~~add configuration option so this is disabled by default~~
- ~~fix whatever weirdness is preventing this working with CSP (even in debug)~~
- ~~use our standard templating mechanism going through apiutil helper func~~
- ~~probably some absurdly small performance improvements to be made in pooling re-used hex encode / hash encode buffers~~ the web endpoints aren't as hot a path as API / ActivityPub, will leave as-is for now as it is already very minimal and well optimized
- ~~verify the cryptographic assumptions re: using a portion of token as challenge data~~ this isn't a serious application of cryptography, if it turns out to be a problem we'll fix it, but it definitely should not be easily possible to guess a SHA256 hash from the first 1/4 of it even if mathematically it might make it a bit easier
- ~~theme / make look nice??~~
- ~~add a spinner~~
- ~~add entry in example configuration~~
- ~~add documentation~~

Verification page originally based on https://github.com/LucienV1/powtect

Co-authored-by: tobi <tobi.smethurst@protonmail.com>
Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4043
Reviewed-by: tobi <tsmethurst@noreply.codeberg.org>
Co-authored-by: kim <grufwub@gmail.com>
Co-committed-by: kim <grufwub@gmail.com>

web/source/nollamas/index.js

@@ -0,0 +1,63 @@
+/*
+	GoToSocial
+	Copyright (C) GoToSocial Authors admin@gotosocial.org
+	SPDX-License-Identifier: AGPL-3.0-or-later
+
+	This program is free software: you can redistribute it and/or modify
+	it under the terms of the GNU Affero General Public License as published by
+	the Free Software Foundation, either version 3 of the License, or
+	(at your option) any later version.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU Affero General Public License for more details.
+
+	You should have received a copy of the GNU Affero General Public License
+	along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+document.addEventListener('DOMContentLoaded', function() {
+	// Get the nollamas section container.
+	const nollamas = document.querySelector(".nollamas");
+
+	// Add some "loading" text to show that
+	// a proof-of-work captcha is being done.
+	const p = this.createElement("p");
+	p.className = "nollamas-explanation";
+	p.appendChild(document.createTextNode("Your browser is currently solving a proof-of-work challenge designed to deter \"ai\" scrapers. This should take no more than a few seconds..."));
+	nollamas.appendChild(p);
+
+	// Add a loading spinner as well if motion is allowed.
+	if (!window.matchMedia('(prefers-reduced-motion: reduce)').matches) {
+		const i = this.createElement("i");
+		i.className = "fa fa-2x fa-spin fa-refresh nollamas-solving";
+		i.setAttribute("title","Solving...");
+		nollamas.appendChild(i);
+	}
+
+	// Read the challenge and difficulty from
+	// data attributes on the nollamas section.
+	const challenge = nollamas.dataset.nollamasChallenge;
+	const difficulty = nollamas.dataset.nollamasDifficulty;
+
+	console.log('challenge:', challenge);   // eslint-disable-line no-console
+	console.log('difficulty:', difficulty); // eslint-disable-line no-console
+
+	// Prepare the worker with task function.
+	const worker = new Worker("/assets/dist/nollamasworker.js");
+	worker.postMessage({
+		challenge: challenge,
+		difficulty: difficulty,
+	});
+
+	// Set the main worker function.
+	worker.onmessage = function (e) {
+		if (e.data.done) {
+			console.log('solution found for:', e.data.nonce); // eslint-disable-line no-console
+			let url = new URL(window.location.href);
+			url.searchParams.set('nollamas_solution', e.data.nonce);
+			window.location.href = url.toString();
+		}
+	};
+});