background.js

const WHITELIST = [
  'https://cdn.theathletic.com'
]

const ALLOW = { cancel: false };
const DENY = { cancel: true };

chrome.webRequest.onBeforeSendHeaders.addListener((req) => {
  var cancel = null;

  if (req.type == 'document') {
    return ALLOW;
  }

  const whitelisted = WHITELIST.find(item => req.url.startsWith(item));

  if (whitelisted) {
    return ALLOW;
  }

  req.requestHeaders.forEach((header, i) => {
    if (header.name == 'Referer' && header.value.startsWith('https://theathletic.com')) {
      cancel = true;
    }
  });

  if (cancel) {
    return DENY;
  }
},
  { urls: ['<all_urls>'] },
  ['blocking', 'requestHeaders']
);