Thanks for you answer.

I meant that I need to restrict access to single wordpress page (there is a secret form there).
/secret-page/ - is a permalink of the page, rewritten URL managed by wordpress.

To make it work I used general config for wordpress I found on DigitalOcean guide
server {
listen 80 default_server;
listen [::]:80 default_server ipv6only=on;

root /var/www/html;
index index.php index.html index.htm;

server_name your_domain.com;

location / {
# try_files $uri $uri/ =404;
try_files $uri $uri/ /index.php?q=$uri&$args;
}

error_page 404 /404.html;

error_page 500 502 503 504 /50x.html;
location = /50x.html {
root /usr/share/nginx/html;
}

location ~ \.php$ {
try_files $uri =404;
fastcgi_split_path_info ^(.+\.php)(/.+)$;
fastcgi_pass unix:/var/run/php5-fpm.sock;
fastcgi_index index.php;
include fastcgi_params;
}
}