Force auth in nginx except for facebooks crawler.

nginx whitelist for facebook

server{
  satisfy any;

  # https://developers.facebook.com/docs/ApplicationSecurity/#facebook_scraper
  allow 31.13.24.0/21;
  allow 31.13.64.0/18;
  allow 66.220.144.0/20;
  allow 69.63.176.0/20;
  allow 69.171.224.0/19;
  allow 74.119.76.0/22;
  allow 103.4.96.0/22;
  allow 173.252.64.0/18;
  allow 204.15.20.0/22;
  allow 2401:db00::/32;
  allow 2620:0:1c00::/40;
  allow 2a03:2880::/32;

  deny all;

  auth_basic            "Restricted";
  auth_basic_user_file  /etc/nginx/.htpasswd;
  # ...
}