Using valid cert for private network

Forgot who said finding some way using cert without NAT
finally i find some way to do it
but pfsense help me spelled some magic
i am not professional on network / security
i only can explain it like I'm 65535, who can explain it to 5?
sorry for poor articles and English

tl;dr

You need

• DNS Resolver
• Public domain name
• Some thing like Let's Encrypt

Step

1. Create subdomain and cert it

Because it's valid CA, it will show valid in browser

2. Create Host Overrides on your DNS Resolver

Because cert will check your domain name and actual domain in url
You must using Step 1 subdomain name

3. Set your server using subdomain cert

Reference

SSL Certificates for Local IP address