By default app checks if $_SERVER['HTTPS']=='on' and if it's enabled then all urls will be under https.

If your server can't detect $_SERVER['HTTPS'] variable then go to config/server.php file and enable SSL mode in ENABLE_SSL variable.

define('ENABLE_SSL', true);

Redirect HTTP to HTTPS automatically

Open .htaccess in folder where app is installed and add following code:

RewriteEngine On
RewriteCond %{HTTPS} off
RewriteRule ^(.*)$ https://%{HTTP_HOST}%{REQUEST_URI} [L,R=301]

These common rules that will work for most of server. But sometimes server can have different setup and if code above will not work then ask your hosting support about .httaccess rules to to redirect from http to https.