force http redirect to https nginx + Nuxt.js

Question

I am deploying an application made with nuxt.js, as hosting I am using digitalocean + serverpilot.

I'm having trouble not to enable SSL but to force redirection from HTTP to HTTPS

below is the nginx setting I'm using

map $sent_http_content_type $expires {
    "text/html"                 epoch;
    "text/html; charset=utf-8"  epoch;
    default                     off;
}
server {
    listen 80;
    server_name            admin.domain.com;

    gzip            on;
    gzip_types      text/plain application/xml text/css application/javascript;
    gzip_min_length 1000;

    location / {
        expires $expires;
        proxy_redirect                      off;
        proxy_set_header Host               $host;
        proxy_set_header X-Real-IP          $remote_addr;
        proxy_set_header X-Forwarded-For    $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto  $scheme;
        proxy_read_timeout          1m;
        proxy_connect_timeout       1m;
        proxy_pass                          http://127.0.0.1:3000;
    }
}
server {
    listen    443 ssl default_server;
    listen    [::]:443 ssl default_server;
    ssl_certificate_key    ssl/_default.key;
    ssl_certificate        ssl/_default.crt;
    return    444;
}

if i turn on https://admin.domain.com it works

if I go to http://admin.domain.com it does not redirect to https and i get unsecured warning

NOTE: I would like to configure inside the server block because in future I will have other servers, for example blog.domain.com