docs: static Secret decrypt(String data, CryptoConfidentialKey key) throws IOException, GeneralSecurityException {
          byte[] in;
          try {
              in = Base64.getDecoder().decode(data.getBytes(StandardCharsets.UTF_8));
          } catch (IllegalArgumentException ex) {
              throw new IOException("Could not decode secret", ex);
          }
          Secret s = tryDecrypt(key.decrypt(), in);
          if (s!=null)    return s;
  
          // try our historical key for backward compatibility
          Cipher cipher = Secret.getCipher("AES");
          cipher.init(Cipher.DECRYPT_MODE, getLegacyKey());
          return tryDecrypt(cipher, in);
      }