Add client ALTCHA proof-of-work and Vite env flags for uploads.

Expose enabled/max-number settings and wire altcha-lib for per-upload challenges.

frontend/src/stores/altcha.ts

@@ -0,0 +1,70 @@
+import { solveChallengeWorkers } from 'altcha-lib/v1';
+import type { Challenge, Payload } from 'altcha-lib/v1/types';
+import { defineStore } from 'pinia';
+import { config } from '@/config';
+import { api } from '@/plugins/axios';
+import { bytesToBase64 } from '@/utils/encoding/bytesToBase64';
+import AltchaSolveWorker from 'altcha-lib/v1/worker?worker';
+
+export const useAltchaStore = defineStore('altcha', () => {
+    const runProofOfWork = async (): Promise<string | undefined> => {
+        if (!config.altcha.enabled) {
+            return undefined;
+        }
+
+        const challenge = await fetchChallenge();
+
+        return encodeSolvedChallenge(challenge);
+    };
+
+    const fetchChallenge = async (): Promise<Challenge> => {
+        const { data } = await api.get<Challenge>('/altcha/challenge');
+
+        return data;
+    };
+
+    const encodeSolvedChallenge = async ({
+        algorithm,
+        challenge: challengeValue,
+        salt,
+        signature,
+        maxnumber
+    }: Challenge): Promise<string> => {
+        const { maxNumber: fallbackMaxNumber } = config.altcha;
+
+        const maxNumber = maxnumber ?? fallbackMaxNumber;
+        const cuncurrency = Math.min(8, Math.max(1, navigator.hardwareConcurrency ?? 4));
+
+        const solution = await solveChallengeWorkers(
+            () => new AltchaSolveWorker(),
+            cuncurrency,
+            challengeValue,
+            salt,
+            algorithm,
+            maxNumber
+        );
+
+        if (!solution) {
+            throw new Error('ALTCHA proof of work could not be solved');
+        }
+
+        const payload: Payload = {
+            algorithm,
+            challenge: challengeValue,
+            number: solution.number,
+            salt,
+            signature
+        };
+
+        const json = JSON.stringify(payload);
+
+        const textEncoder = new TextEncoder();
+        const bytes = textEncoder.encode(json);
+
+        return bytesToBase64(bytes);
+    };
+
+    return {
+        runProofOfWork
+    };
+});