Selenium Webdriver headless chrome with proxy authentication

I need to use an authenticated proxy with my headless implementation of chrome. These are jobs that get executed on heroku dynos (if there's maybe a better way to implement a proxy directly on heroku dynos).

If I follow standard proxy implementations for selenium I get stuck at the authentication page where it asks for a username / password.

This is how I instantiate a headless chrome instance with watir & selenium:

def headless_browser
  options = Selenium::WebDriver::Chrome::Options.new

  # make a directory for chrome if it doesn't already exist
  chrome_dir = File.join Dir.pwd, %w(tmp chrome)
  FileUtils.mkdir_p chrome_dir
  options.add_argument "--user-data-dir=#{chrome_dir}"

  # set Random User Agent
  options.add_argument "--user-agent=#{random_user_agent}"

  # let Selenium know where to look for chrome if we have a hint from
  # heroku. chromedriver-helper & chrome seem to work out of the box on osx,
  # but not on heroku.
  if chrome_bin = ENV["GOOGLE_CHROME_BIN"]
    options.add_argument "no-sandbox"
    options.binary = chrome_bin

    # give a hint to webdriver here too
    Selenium::WebDriver::Chrome.driver_path = \
      '/app/vendor/bundle/bin/chromedriver'
  end

  options.add_argument '--allow-insecure-localhost'

  # headless!
  # keyboard entry wont work until chromedriver 2.31 is released
  options.add_argument '--window-size=1200x600'
  options.add_argument '--headless'
  options.add_argument '--disable-gpu'
  options.add_argument '--no-sandbox'

  # instantiate the browser
  browser = Watir::Browser.new :chrome, options: options

  if Rails.env.development?
    browser.goto "https://api.myip.com"
    JSON.parse(Nokogiri::HTML.parse(browser.html).css('body').text)
  end
end

Does anyone have any idea how to implement authenticated proxy usage with watir & selenium? I searched a lot and implemented a lot of different "solutions" but none worked for me.

• Tried setting a proxy via the selenium driver. If just left like this the authentication window pops up and I can't access that.

Selenium::WebDriver::Proxy.new(
  http: '127.0.0.1:8080',
  ssl:  '127.0.0.1:8080'
)

I also tried the socks format: username:password@host:port. Didn't work.

• I tried setting the --proxy-server= option to the driver. While it works with the plain proxy url, it behaves just like the above.