ESP secure connection

Hello,

There is a shared library in ESP8266 for secure connection over TLS. Called SecureWifiClient.

To verify digital certification the Esp must validate the certification ia not expired by the valida from and valid untill fields of certification.
My question is how the esp know what is the date to determinf if the date is too old or too new?
I mean we dont have system clock like we have in operation system.

Thanks