Ruby

#!/usr/bin/env node
const puppeteer = require('puppeteer');

(async () => {
  const browser = await puppeteer.launch({
                    args: ['--proxy-server=https://isp.joinmassive.com:4080']
                  });
  const page    = (await browser.pages())[0];

  await page.authenticate({
    username: '{PROXY_USERNAME},
    password: '{API_KEY}'
  });
  await page.goto('https://cloudflare.com/cdn-cgi/trace'); // Insert your target URL here
  console.log(await page.content());
  browser.close();
})();