Infrastructure build to support third-party app integrations

backend/lib/crypto.ts

@@ -0,0 +1,77 @@
+import {
+  createCipheriv,
+  createDecipheriv,
+  createHash,
+  randomBytes,
+  timingSafeEqual,
+} from 'node:crypto';
+
+const ALGORITHM = 'aes-256-gcm';
+const IV_BYTES = 12;
+const KEY_BYTES = 32;
+
+const loadKey = (): Buffer => {
+  const raw = process.env.TOKEN_ENCRYPTION_KEY;
+  if (!raw) {
+    throw new Error('TOKEN_ENCRYPTION_KEY is not set');
+  }
+
+  const key = Buffer.from(raw, 'base64');
+  if (key.length !== KEY_BYTES) {
+    throw new Error(
+      `TOKEN_ENCRYPTION_KEY must decode to ${KEY_BYTES} bytes, got ${key.length}`
+    );
+  }
+
+  return key;
+};
+
+/** Serialized as base64(iv):base64(authTag):base64(ciphertext). */
+export const encryptSecret = (plaintext: string): string => {
+  const iv = randomBytes(IV_BYTES);
+  const cipher = createCipheriv(ALGORITHM, loadKey(), iv);
+
+  const payload = Buffer.concat([
+    cipher.update(plaintext, 'utf8'),
+    cipher.final(),
+  ]);
+
+  return [
+    iv.toString('base64'),
+    cipher.getAuthTag().toString('base64'),
+    payload.toString('base64'),
+  ].join(':');
+};
+
+export const decryptSecret = (ciphertext: string): string => {
+  const parts = ciphertext.split(':');
+  if (parts.length !== 3) {
+    throw new Error('Ciphertext is not in the expected iv:tag:payload form');
+  }
+
+  const [iv, tag, payload] = parts;
+  const decipher = createDecipheriv(
+    ALGORITHM,
+    loadKey(),
+    Buffer.from(iv, 'base64')
+  );
+  decipher.setAuthTag(Buffer.from(tag, 'base64'));
+
+  return Buffer.concat([
+    decipher.update(Buffer.from(payload, 'base64')),
+    decipher.final(),
+  ]).toString('utf8');
+};
+
+export const hashApiKey = (key: string): string =>
+  createHash('sha256').update(key, 'utf8').digest('hex');
+
+/**
+ * Constant-time string comparison. Both sides are hashed first so that
+ * unequal lengths cannot short-circuit the comparison or throw.
+ */
+export const safeEquals = (a: string, b: string): boolean => {
+  const digestA = createHash('sha256').update(a, 'utf8').digest();
+  const digestB = createHash('sha256').update(b, 'utf8').digest();
+  return timingSafeEqual(digestA, digestB);
+};