How to let the backend api handle https certificate? - nginx

Question

I'm new to nginx.
I have a machine, behind my router, that runs a server and handles correctly 80 and 443 request with Https.
Problem is that I want to host a second website on another device but I have only one IP address. I bought a raspberry pi zero to use it as a reverse proxy behind my router. I install nginx and want to redirect all the request to my other machines. Both the RPI 0 and the old machine have local IP.
To redirect requests from my router to RPI 0 and then to my old machine, I used proxy_pass. On port 80 everything works fine, but on port 443 I get a certificate error on my browser.
Is it possible to let the whole request go on the old machine and let the old machine handles the https certificate like before ? Or is it mandatory to have the certificate processed by nginx ?
Diagram of the old but functional installation
Current installation with certificate error
My configuration:
upstream backend_a {
server 192.168.0.20:80;
}
upstream backend_a_s {
server 192.168.0.20:443;
}
server {
listen 80;
server_name mydomain;
location / {
include proxy_params;
proxy_pass http://backend_a;
}
}
server {
listen 443 ssl;
server_name mydomain;
location / {
include proxy_params;
proxy_pass https://backend_a_s;
}
}

Answer 1

I found a solution. I need to use port forwarding. To do this in nginx, I need to use stream keyword.
stream {
server {
listen 443;
proxy_pass 192.168.0.20:443;
}
}
The stream keyword need to be at the same level as http, so I needed to edit /etc/nginx/nginx.conf source. Other solution is to manually compile a version of nginx, with the parameter --with-stream source.