Is there an appropriate tutorial for setting up HTTPS for Vaadin on Debian with Tomcat server?
I am following this one but I don’t get to Installing the certificate to Java keystore, because I’m a noob and I dont know that a Java keystore is and what its password is 
https://vaadin.com/blog/enabling-https-in-your-java-server-using-a-free-certificate
Tomcat documentation may help you
https://tomcat.apache.org/tomcat-9.0-doc/ssl-howto.html
Maybe a better approach would be to handle SSL on a reverse proxy. Is Apache or Nginx running on the server?
Password is what you define it to be 
A suggestion: add a front-proxy to your server and let that handle HTTPS connection. I have been lately using nginx without issues. For that the letsencrypt instructions are bit less crypic 
Now why didn’t Discord show Simon’s same answer before I wrote my own 
Probably Discord likes it when you type something into the chat 
Oh yeah, maybe the developers got a quarterly target to increase the amount of messages with multiple same answers 
They should add some AI 