code: private Fingerprint createFakeFingerprint(String userName) {
      byte[] usernameHmac = CrtAuthCodec.getAuthenticationCode(
          this.secret, userName.getBytes(Charsets.UTF_8));
      return new Fingerprint(Arrays.copyOfRange(usernameHmac, 0, 6));
    }
docs: Generate a fake real looking fingerprint for a non-existent user.
  
  @param userName the username to seed the transform with
  @return a Fingerprint with bytes that are a function of username and secret