In your sites-available -> sites-enabled folder respective website config file

nginxsite.com

server {
  listen       portnumber;
  server_name  ip_address;
  location / {
      root   /var/www/mywebsite.com;
      index  index.html index.htm;
      auth_basic "Restricted";                                #For Basic Auth
      auth_basic_user_file /etc/nginx/.htpasswd;  #For Basic Auth
  }
}