How to buy and attach an SSL certificate for a self-written REST service?

Question

Java

Good afternoon!
Faced a problem.
I have a frontend (Java, Spring) and a backend (angular 4).
I need to add HTTPS for all this.
I added an SSL certificate for the frontend, but I also need to add a certificate for the backend.
And here the question is - how can I buy a certificate for the backend?
After all, when buying certificates, you need to confirm either a domain or something else ... and I have a self-written REST server that runs on a rented virtual server.

Answer 1

1. why do you need ssl in your sandbox, you are burning processor cycles for no reason.
2. issue your certificate and sign your services.
Setting up trust, feedback chains is purely in your hands. However, you can get a wilcard certificate and resolve access at the firewall level or at the level of the application itself, allowing or denying access from a specific host and port

Answer 2

nginx as a proxy and into it a certificate from letsencrypt.