nginx.conf

  # this goes in the http{} block
  # remove any $no_cache "sets" from individual site confs (e.g. ` set $no_cache 0;`)

  # 0 means we cache
  # any other value will negate it

  #check cookie for certain logged-in-type values, if found set 1
  map $http_cookie $no_cookie_cache {
    default 0;
    "~comment_author_|wordpress_(?!test_cookie)|wp-postpass_" 1;
  }

  #check uri for certain logged-in-type values, if found set 1
  #originally used $request_uri, but this includes the query string which makes it easier to bypass accidentally or maliciously
  map $uri $no_uri_cache {
    default 0;
    "~wp-admin|wp-login.php" 2;
  }

  #finally, check if both values are 0 ("00"), any other combo means something should bypass
  map $no_cookie_cache$no_uri_cache $no_cache {
    default 1;
    "00" 0;
  }