example-geo.nginxconf

# This block requires the geo module, which enables the use of
# variables which depend on the IP address of the client.
#
# In this case, everyone outside of the 192.168.0.x network
# is considered an "external" client.
geo $external {
  default 1;
  192.168.0.0/24 0;
}

server {
  listen      192.168.0.1:80;
  server_name example.com;

  # Redirect all requests from the external IPs to an
  # unauthorized page.
  if ($external) {
    rewrite ^ /unauthorized.html last;
  }  

  try_files $uri $uri.html $uri/index.html =404;
}

example.nginxconf

server {
  listen      192.168.0.1:80;
  server_name example.com;

  location / {
    # This line determines the access policy based on multiple
    # access handles, meaning it will let the user pass if any 
    # of the following conditions are fulfilled: 
    #
    # * the IP address belongs to the 192.168.0.x range
    # * the username and password match those on file in users.conf
    satisfy any;

    allow 192.168.0.0/24;
    deny  all;

    auth_basic            "Restricted Access";
    auth_basic_user_file  users.conf;

    try_files $uri $uri.html $uri/index.html =404;
  }
}