Replace {{domain}} with the server domain you set up. This script will change the classname of the body element in a html document to either `tpc-ok` or `tpc-fail` if third-party-cookies are enabled or not. Adopted from https://stackoverflow.com/questions/3550790/check-if-third-party-cookies-are-enabled

tpc.css

.tpc-ok-only {
  display: none;
}
.tpc-fail-only {
  display: none;
}
.tpc-loading {
  display: block;
}
body.tpc-ok .tpc-loading,
body.tpc-fail .tpc-loading {
  display: none;
}
body.tpc-ok .tpc-ok-only {
  display: block;
}
body.tpc-fail .tpc-fail-only {
  display: block;
}

tpc.js

;(function () {
  if (document.getElementById('tpc-test')) {
    // Prevent duplicate execution
    return
  }
  var body = document.body
  var tpcDomain = '//{domain}/'
  var step1 = document.createElement('script')
  step1.setAttribute('src', tpcDomain + 'step1.js')
  var step2 = document.createElement('script')
  step2.setAttribute('src', tpcDomain + 'step2.js')

  window._3rd_party_test_step1_loaded = function () {
    body.classList.add('tpc-step-2')
    body.classList.remove('tpc-step-1')
    body.removeChild(step1)
    body.appendChild(step2)
  }
  window._3rd_party_test_step2_loaded = function (cookieSuccess) {
    body.classList.toggle('tpc-ok', cookieSuccess)
    body.classList.toggle('tpc-fail', !cookieSuccess)
    body.classList.remove('tpc-step-2')
    body.removeChild(step2)
  }

  body.classList.add('tpc-step-1')
  body.appendChild(step1)
})()

{domain}.conf

server {
    listen 80;
    server_name {domain}

    # don't allow user's browser to cache these replies
    expires -1;
    add_header Cache-Control "private";
    etag off;

    location = /step1.js {
        add_header Content-Type 'application/javascript; charset=UTF-8';

        add_header Set-Cookie "third_party_c_t=hey there!;Max-Age=172800";

        return 200 'window._3rd_party_test_step1_loaded();';
    }

    location = /step2.js {
        add_header Content-Type 'application/javascript; charset=UTF-8';

        set $test 'false';
        if ($cookie_third_party_c_t = 'hey there!') {
            set $test 'true';
            # clear the cookie
            add_header Set-Cookie "third_party_c_t=;expires=Thu, 01 Jan 1970 00:00:00 GMT";
        }

        return 200 'window._3rd_party_test_step2_loaded($test);';
    }
}