This is a question / request for clarification

I am trying to make this example work: https://github.com/chrisjoyce911/esp32FOTA/blob/master/examples/HTTP/HTTPS.ino

In the example, it is not clear how to perform this step:
Step 3 : Provide SPIFFS filesystem with root_ca.pem of your webserver

I also checked the README.md - same cryptic instruction "For https or signature check: SPIFFS with root_ca.pem (https) and rsa_key.pem (signature check)"

How does actually one do that ?

Can the certificate check not be managed by a constant in the sketch as described in this article: https://www.lab4iot.com/2021/02/21/esp32-secure-firmware-update-over-the-air-ota/?unapproved=660&moderation-hash=f37b98b9077b522d86cd237ae1a442dc#comment-660

char *siteCertificate =
"-----BEGIN CERTIFICATE-----\n"
...

Many thanks in advance