import asyncio
from pyppeteer import launch


async def main():
    browser = await launch(
        {
            'ignoreHTTPSErrors': True,
            'args': [
                '--proxy-server=proxy.crawlera.com:8011',
                '--ignore-certificate-errors'
            ]
        }
    )
    page = await browser.newPage()
    await page.authenticate({'username': '<API KEY HERE>', 'password': ''})
    await page.goto('https://www.zyte.com/', {'timeout': 180000})
    await page.screenshot({'path': 'zyte.png'})
    await browser.close()

asyncio.get_event_loop().run_until_complete(main())


Tested with pyppeteer==0.2.5.