Protect Jenkins with nginx http auth except callback url

I installed jenkins on my server and I want to protected it with nginx http auth so that requests to:

http://my_domain.com:8080
http://ci.my_domain.com

will be protected except one location:

http://ci.my_domain.com/job/my_job/build

needed to trigger build. I am kinda new to nginx so I stuck with nginx config for that.

upstream jenkins {
  server  127.0.0.1:8080;
}

server {
  listen x.x.x.x:8080;
  server_name *.*;

  location '/' {
    proxy_pass http://jenkins;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Host $http_host;
    proxy_redirect off;

    auth_basic "Restricted";
    auth_basic_user_file /path/.htpasswd;    
  }
}

I tried smth like above config but when I visit http://my_domain.com:8080 there is no http auth.