default

sudo nano /etc/nginx/sites-enabled/default

# Add
server {
    listen 80;
    server_name example.com; # Your site

    proxy_buffering off;

    location / {
        auth_basic "Home Assistant";
        auth_basic_user_file /etc/nginx/.htpasswd; # Your .htpasswd file
        proxy_pass http://127.0.0.1:8123/; # The server you want to redirect to
        proxy_set_header Host $host;
    }
}