Initial Kelola Bumi website

lib/contact-captcha.ts

@@ -0,0 +1,54 @@
+import crypto from "node:crypto";
+
+const CAPTCHA_TTL_MS = 10 * 60 * 1000;
+
+function getSecret() {
+  return process.env.CONTACT_CAPTCHA_SECRET ?? "fallback-contact-captcha-secret";
+}
+
+export function generateCaptchaChallenge() {
+  const left = crypto.randomInt(1, 10);
+  const right = crypto.randomInt(1, 10);
+  const answer = left + right;
+  const expiresAt = Date.now() + CAPTCHA_TTL_MS;
+  const payload = `${answer}:${expiresAt}`;
+  const signature = crypto
+    .createHmac("sha256", getSecret())
+    .update(payload)
+    .digest("hex");
+
+  return {
+    prompt: `${left} + ${right} = ?`,
+    token: `${payload}:${signature}`
+  };
+}
+
+export function verifyCaptchaToken(token: string, answer: string) {
+  const parts = token.split(":");
+  if (parts.length !== 3) {
+    return false;
+  }
+
+  const [expectedAnswer, expiresAt, signature] = parts;
+  const payload = `${expectedAnswer}:${expiresAt}`;
+  const expectedSignature = crypto
+    .createHmac("sha256", getSecret())
+    .update(payload)
+    .digest("hex");
+
+  const isSignatureValid = crypto.timingSafeEqual(
+    Buffer.from(signature),
+    Buffer.from(expectedSignature)
+  );
+
+  if (!isSignatureValid) {
+    return false;
+  }
+
+  if (Number(expiresAt) < Date.now()) {
+    return false;
+  }
+
+  return expectedAnswer === answer.trim();
+}
+