addCookies()

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

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

export default async function () {
  const context = browser.newContext();
  const page = context.newPage();

  try {
    const unixTimeSinceEpoch = Math.round(new Date() / 1000);
    const day = 60*60*24;
    const dayAfter = unixTimeSinceEpoch+day;
    const dayBefore = unixTimeSinceEpoch-day;

    context.addCookies([
      // this cookie expires at the end of the session
      {
        name: 'testcookie',
        value: '1',
        sameSite: 'Strict',
        domain: 'httpbin.org',
        path: '/',
        httpOnly: true,
        secure: true,
      },
      // this cookie expires in a day
      {
        name: 'testcookie2',
        value: '2',
        sameSite: 'Lax',
        domain: 'httpbin.org',
        path: '/',
        expires: dayAfter,
      },
      // this cookie expires in the past, so it will be removed.
      {
        name: 'testcookie3',
        value: '3',
        sameSite: 'Lax',
        domain: 'httpbin.org',
        path: '/',
        expires: dayBefore
      }
    ]);

    const response = await page.goto('https://httpbin.org/cookies', {
      waitUntil: 'networkidle',
    });
    console.log(response.json());
    // prints:
    // {"cookies":{"testcookie":"1","testcookie2":"2"}}
  } finally {
    page.close();
  }
}