Arduino Opta HTTPS Client Setup

I need a working example that lets my Arduino Opta act as an HTTPS client and reach a remote API endpoint over a fully encrypted connection. There is no extra authentication layer—once the TLS handshake is in place the request can be sent over the encrypted connection. The API endpoint is on a server with NGINX. The connection needs to work for 20 years. Update of the Arduino Opta module to update certificates is not possible. So self signed certificates are necessary.

The main objective is to make sure the Opta module connects to the correct NGINX server and hide the content of the message for tools like wireshark.

Please build and document a minimal but complete sketch that compiles in the standard Arduino IDE, shows the certificate handling, performs a simple GET and a test POST, and prints the returned JSON to Serial. Include any helper libraries you use (WiFiClientSecure, mbedTLS-based forks, etc.) and note the exact versions so I can reproduce the build.

Please provide a guide how to setup the NGINX site to accept the Opta connection, please include examples how to create the certificate for the specific URL.

Deliverables
• Arduino Opta sketch with all required includes
• Step-by-step instructions for loading certificates and flashing the board
• A brief README explaining how I change the endpoint URL and recompile
• Proof-of-success screenshots or Serial logs showing a 200 OK from the API

I will consider the job complete when I can load your code, change the URL to my own API, and watch the Opta retrieve data over HTTPS without errors.