To test a page protected by HTTP Basic authentication with BackstopJS, use its Puppeteer engine and an onBeforeScript hook that calls await page.authenticate({ username, password }) before navigation. Keep credentials in environment variables or your CI secret store, not in backstop.json or source control.
Configure BackstopJS to authenticate before navigation
BackstopJS provides the browser page to its custom hook for per-scenario setup. Puppeteer’s Page.authenticate() supplies HTTP-auth credentials. The following is a setup example adapted from those documented APIs; it is guidance, not code reported as executed or tested. The BackstopJS README accessed October 3, 2026 identifies Puppeteer as the default engine, though it does not specify a fixed release number.
1. Add the scenario and hook
{
"engine": "puppeteer",
"onBeforeScript": "auth.js",
"scenarios": [
{
"label": "Protected page",
"url": "https://staging.example.test/protected",
"readySelector": "main"
}
]
}Save this as the relevant BackstopJS configuration, commonly backstop.json. If your project stores engine scripts somewhere other than the default, set paths.engine_scripts to point to that directory. A scenario can override the root hook when it needs different setup.
2. Create the authentication script
Place auth.js in the configured engine scripts directory (commonly backstop_data/engine_scripts/auth.js):
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module.exports = async (page) => {
const username = process.env.BASIC_AUTH_USER;
const password = process.env.BASIC_AUTH_PASSWORD;
if (!username || !password) {
throw new Error('Set BASIC_AUTH_USER and BASIC_AUTH_PASSWORD');
}
await page.authenticate({ username, password });
};BackstopJS documents the hook signature as onBefore(page, scenario, viewport, isReference, Engine, config); this example uses the supplied page. Define BASIC_AUTH_USER and BASIC_AUTH_PASSWORD in your local shell or CI secret store before running BackstopJS. The explicit check turns a missing secret into a clear setup error rather than a confusing unauthenticated capture.
Make the capture useful for visual regression
Wait for authenticated content
A successful authentication response does not guarantee that a client-rendered page has finished rendering. Use a readySelector that appears in the authenticated content, as in the example, or configure a suitable readyEvent. BackstopJS also supports a delay; an observable readiness condition is preferable when the application exposes one.
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Choose the region under test
BackstopJS supports capturing the full document, the viewport, or explicit CSS selectors. Choose the region that matches the visual behavior the test is meant to protect: a viewport can miss content below the fold, while a full-page image can include unrelated sections that make comparisons noisier.
Review reference changes deliberately
BackstopJS compares test screenshots against reference images. Inspect its visual report before approving changed references: approval updates the reference images used by later comparisons. Do not approve a change merely to make a failing test green until you have confirmed the page is in the expected authenticated state and the visual difference is intended.
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Choose the engine based on the authentication state
| Engine | Relevant documented setup | When it fits |
|---|---|---|
| Puppeteer | BackstopJS identifies it as the default engine in its current README; Puppeteer’s page.authenticate() supplies HTTP-auth credentials. |
Use for HTTP Basic authentication with the hook shown above. |
| Playwright | BackstopJS documents a Playwright engine and corresponding scripts. Its documented storageState restores cookies and localStorage. |
Use when the project is configured for Playwright, or when the required state is a saved browser session. The cited BackstopJS guidance does not establish that storageState supplies HTTP Basic credentials. |
If you switch to Playwright, follow BackstopJS’s Playwright engine and script configuration rather than assuming a Puppeteer hook works unchanged. Confirm the HTTP-auth method against the current Playwright API documentation for the version installed in your project; the BackstopJS material cited here does not document that engine-specific method.
Troubleshoot authentication and capture failures
- You see a 401 response or browser authentication prompt: Confirm both environment variables are present in the process running BackstopJS, that the credentials are correct, and that the hook is configured for the scenario. Verify that the protected URL is the intended one.
- You land on a separate sign-in form: This is likely form-based authentication, not HTTP Basic.
page.authenticate()handles HTTP authentication and will not fill in a web form. Use a deliberate login interaction or restore an appropriate session state instead. - The capture happens before the page is ready: Replace an arbitrary delay, where possible, with a
readySelectororreadyEventtied to authenticated content. Check that the selector is present on the authenticated page, not just on a login or error screen. - The hook cannot be found: Check
paths.engine_scriptsand the script filename. Verify the configuration against the BackstopJS version and engine actually installed; older releases or custom engines may differ. - The screenshot compares the wrong area: Revisit the scenario’s capture selection—
document,viewport, or CSS selectors—and inspect the visual report before accepting reference updates. - Authentication makes runs slower: Puppeteer notes that authentication enables request interception behind the scenes and may affect performance. Treat this as a possible cost of the authentication setup, not a quantified slowdown.
Or skip the browser setup
If you need a screenshot rather than a BackstopJS visual-regression workflow, ScreenshotNeo is a website screenshot API with a single GET request. For a publicly reachable page, a basic request looks like this (see the API documentation):
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