lost like whole day making this work

rails-cookie-hell.ts

import crypto from 'crypto';

export const decryptRailsCookie = (cookie: string): string | undefined => {
  const secret = process.env.SESSIONS_SECRET as string;
  let cookieBuffer = Buffer.from(cookie, 'base64').toString();

  if (cookieBuffer.indexOf('--') === -1) {
    cookieBuffer = cookie;
  }

  const [encryptedData, iv] = cookieBuffer
    .split('--')
    .map((e) => Buffer.from(e, 'base64'));

  const SALT = 'encrypted cookie';
  const ALGO = 'aes-256-cbc';
  const KEY_LENGTH = 32;
  try {
    const KEY = crypto.pbkdf2Sync(
      Buffer.from(secret, 'utf-8'),
      Buffer.from(SALT, 'utf-8'),
      1000,
      KEY_LENGTH,
      'SHA1',
    );
    const cipher = crypto.createDecipheriv(ALGO, KEY, iv);
    cipher.setAutoPadding(true);
    const result = Buffer.concat([
      cipher.update(encryptedData),
      cipher.final(),
    ]);
    return result.toString('utf-8');
  } catch (err) {
    return undefined;
  }
};

export const encryptRailsCookie = (str: string): string => {
  const secret = process.env.SESSIONS_SECRET as string;

  const SALT = 'encrypted cookie';
  const ALGO = 'aes-256-cbc';
  const KEY_LENGTH = 32;
  const iv = crypto.randomBytes(16);
  const KEY = crypto.pbkdf2Sync(
    Buffer.from(secret, 'utf-8'),
    Buffer.from(SALT, 'utf-8'),
    1000,
    KEY_LENGTH,
    'SHA1',
  );
  const cipher = crypto.createCipheriv(ALGO, KEY, iv);
  cipher.setAutoPadding(true);
  const encrypted = Buffer.concat([cipher.update(str), cipher.final()]);
  return `${encrypted.toString('base64')}--${iv.toString('base64')}`;
};