Self-Signed Certificate Installation [Solved?]

I followed the Installation instruction for setting up a self-signing certificate on Ubuntu (I have Mint): See https://docs.nextcloud.com/server/12/admin_manual/installation/source_installation.html#enabling-ssl-label

Basically it’s supposed to be as simple as:

a2enmod ssl
a2ensite default-ssl
service apache2 reload

This didn’t appear to be working until I typed in https://192.168.x.x/nextcloud into the URL bar and added a self-signed security exception. It appears to work fine in Firefox, but not in Chromium. Anyway, I think it’s working but any comments much appreciated.

FWIW I really don’t think I need to deal with letsencrypt etc because I don’t want the public on my system anyway.

I found some further information here: https://docs.nextcloud.com/server/12/admin_manual/configuration_server/harden_server.html
QUOTE

Redirect all unencrypted traffic to HTTPS

To redirect all HTTP traffic to HTTPS administrators are encouraged to issue a permanent redirect using the 301 status code. When using Apache this can be achieved by a setting such as the following in the Apache VirtualHosts configuration:

<VirtualHost *:80>
   ServerName cloud.nextcloud.com
   Redirect permanent / https://cloud.nextcloud.com/
</VirtualHost>

Enable HTTP Strict Transport Security

While redirecting all traffic to HTTPS is good, it may not completely prevent man-in-the-middle attacks. Thus administrators are encouraged to set the HTTP Strict Transport Security header, which instructs browsers to not allow any connection to the Nextcloud instance using HTTP, and it attempts to prevent site visitors from bypassing invalid certificate warnings.

This can be achieved by setting the following settings within the Apache VirtualHost file:

<VirtualHost *:443>
   ServerName cloud.nextcloud.com
    <IfModule mod_headers.c>
       Header always set Strict-Transport-Security "max-age=15552000; includeSubDomains"
     </IfModule>
  </VirtualHost>

UNQUOTE

Can someone tell me what files to actually put this code into? I have Linux Mint 18.2?