Browser automation: Playwright and Puppeteer

Headless browsers authenticate to a proxy differently than curl or an HTTP client library: the username and password are passed as separate fields, not embedded in a single URL. The username field is still the full login string, your opaque username plus whatever _loc_<CODE> and _sticky suffixes you want, exactly as described in Rotating vs sticky sessions and location targeting.

Browser proxy support is built around HTTP proxies with authentication, that's the well-supported path for both tools below. Use the HTTP endpoint (proxy.masklabs.io:8080) for browser automation.

Playwright

npm install -D playwright

import { chromium } from 'playwright'

const browser = await chromium.launch({
  proxy: {
    server: 'http://proxy.masklabs.io:8080',
    username: 'mlabs_a1f9c3_sticky',
    password: '<PASSWORD>',
  },
})
const page = await browser.newPage()
await page.goto('https://ipinfo.io/json')

server is just protocol://host:port, the credential goes in username and password, not in the URL. Chromium and Firefox also accept a proxy option per browser context (browser.newContext({ proxy: {...} })), so you can hand different tabs different credentials or _loc_ targets without relaunching the browser.

Puppeteer

npm install puppeteer

import puppeteer from 'puppeteer'

const browser = await puppeteer.launch({
  args: ['--proxy-server=proxy.masklabs.io:8080'],
})
const page = await browser.newPage()
await page.authenticate({
  username: 'mlabs_a1f9c3_sticky',
  password: '<PASSWORD>',
})
await page.goto('https://ipinfo.io/json')

Puppeteer sets the proxy at launch (as a Chromium flag) and authenticates it per-page with page.authenticate, the username there is the same full login string, suffixes included.

Sticky sessions for logins

A login or checkout flow that spans several page loads should stay on one exit IP for the whole flow, or the target may see the session cookie arrive from a different IP mid-flow and kill it. Use one _sticky credential for that flow and keep the same login string for every request the browser makes, don't mix a rotating credential into the middle of it.

_sticky pins for about 60 seconds (see Rotating vs sticky sessions and location targeting for the full mechanics); most login and checkout flows complete well inside that window.

SOCKS5 in a browser

Stick to the HTTP endpoint for automation. Authenticated SOCKS5 proxies aren't reliably supported by Chromium's built-in proxy client the way HTTP proxy auth is, the HTTP gateway (:8080) gives you the same rotating, sticky, and location suffixes with dependable auth support in both tools above.