Google Authenticator on Nginx

Question

I built Nginx with ngx_http_auth_pam_module and edited Nginx configurations and /etc/pam.d/nginx like this

Part of virtual host setting

location / {
    root   /projects/admin;
    index  index.html index.htm;
    auth_pam "Google Authenticator Code Required";
    auth_pam_service_name "nginx";
}

/etc/pam.d/nginx

auth required pam_google_authenticator.so

Why can't I authorize by the Google Authenticator? Please help me.