In this article, the author demystifies the business of encrypting and decrypting network traffic, and translates arcane terms such as https, ssh, sftp, etc.
The Common Name (also CN) identifies the host name associated with the certificate, for example www.example.com or example.com.
It consists of a single host name in case of a single-name certificate (e.g. example.com, www.example.com), or a wildcard name in case of a wildcard certificate (e.g. *.example.com). In all cases, it is not an URL and therefore it doesn’t include any protocol (e.g. http:// or https://), port number, or pathname.
The overhead is due to the SSL handshakes, which are lengthy and drastically increase the number of round-trips required for a HTTPS session over a HTTP one.
For an easier alternative to using these example, the [ESP8266HTTPClient library](https://github.com/esp8266/Arduino/tree/master/libraries/ESP8266HTTPClient) can be used (which also supports HTTPS via a SHA1 fingerprint).
HTTPClient library supports https using a fingerprint (SHA1) which can be extracted from the browser. This hash is outdated and should be replaced at some point. For now it is the easiest way to do a HTTPS request. Another option might be using a [using CA certificate via the WiFiClientSecure library](https://github.com/esp8266/Arduino/blob/master/libraries/ESP8266WiFi/examples/HTTPSRequestCACert/HTTPSRequestCACert.ino).