setExtraHTTPHeaders(headers)

import { browser } from 'k6/experimental/browser';

export const options = {
  scenarios: {
    browser: {
      executor: 'shared-iterations',
      options: {
        browser: {
            type: 'chromium',
        },
      },
    },
  },
}

export default async function () {
  const page = browser.newPage();
  
  page.setExtraHTTPHeaders({ 'foo': 'bar' });
  const url = await page.goto('https://test.k6.io/browser.php');

  console.log(url.request().headers().foo) // prints bar
}