How to secure connection between two applications?

Question

Python

Hello!
Essence of the question: There is an api server (node ​​js) that receives commands from the front (react) and must then send this command for execution directly to the Linux machine. (In the daemon scheme). So it's already written in python.
Everything works with each other via rest api. So this is how I can secure(encrypt) data between api and daemon.
So that no one can pass the command to the daemon for execution (It performs specific actions on the server, so you need to protect it as much as possible)

Answer 1

VPN not? As if it is intended for this.
In general, this is the task of the system administrator, so that endpoints from daemons do not look into the open network.

Answer 2

JWT + SSL

Answer 3

And why, in fact, do you have data after the frontend going over such a network that encryption is required?
Even if this is some kind of geographically distributed structure, it is usually combined into a secure virtual local area network. If everything is so bad that there is nothing to raise the VPN on, then if it is HTTP, the option with TLS suggests itself.