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Deploy a Cloudflare Worker to sanely score users' new passwords with zxcvbn AND check for matches against haveibeenpwned's 10+ billion breached accounts


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Enlist a Cloudflare Worker as your Secure Password Scoring and Pwnage Protection API

(Prefer traditional serverless sorcery? See the AWS Lambda version here)

Deploy a private, secure and serverless RESTful endpoint for sanely scoring users' new passwords using Dropbox's zxcvbn library while (k-)anonymously querying Troy Hunt's haveibeenpwned collection of +10 billion breached accounts.

API in Action

    Example: handling results with VuetifyJS


People seemed to think this concept was neat, and a tiny RESTful API like this is a perfect use case for Cloudflare Workers.

As a bonus, over 90% of pwnedpassword queries are already cached on Cloudflare's edge, making response times spooky fast 👻

Quick Start

  1. Rename example.cloudflare.env to cloudflare.env and edit the configuration as needed.
  2. Install deps with npm install
  3. Launch 🚀 with npm run deploy


The following options are configurable via cloudflare.env:

  • ROUTE_PATTERN: Optionally include a route-matching pattern for your worker. See example.cloudflare.env for details on how patterns are parsed and applied (default: undefined)

  • ALLOWED_ORIGIN: Whitelisted origin for Cross Origin Resource Sharing. If not provided, all origins are allowed (default: *)

  • ALLOWED_ORIGIN_PATTERNS: Comma-seperated list of strings to be converted to RegExp patterns for testing the incoming request origin. If the origin matches, it's returned as allowed. If no pattern is matched, CORS falls back to the configured ALLOWED_ORIGIN (default: undefined)

    • Example: "(foo|bar|buzz)\.example\.lol,yet\.another\.example\.omg"
  • CORS_MAXAGE: Value in seconds for the Access-Control-Max-Age CORS header (default: "300")

  • ALWAYS_RETURN_SCORE: Return the zxcvbn score even if the pwnedpasswords match value is > 0. See Response for details (default: undefined, thereby false)

  • CUSTOM_PW_DICT: Comma-seperated list of words/phrases to be included in the zxcvbn strength estimation dictionary. It's a good idea to include e.g. your company or application name here (default: '')

  • RETURN_PW_METADATA: Return the full result of the zxcvbn strength estimation as a metadata response key. Refer to the zxcvbn documentation for details on what that includes (default: undefined, thereby false)


Update configuration à la changes to cloudflare.env by re-running npm run deploy.

NOTE: For reasons unknown, the Cloudflare Dash may continue to show older scripts after a successful upload. Check the x-worker-last-modified response header to verify that your latest script is up and running.


POST user password input to your route as JSON with field password like so:

// pwned password
  "password": "monkey123"
// stronger password
  "password": "wonderful waffles"


Our little worker-bro will reply with an appropriate status code, and JSON body with ok indicating successful scoring and range search, a strength estimation score of 0 through 4 per zxcvbn, and pwned matches, indicating the number times the input appears in the haveibeenpwned database.

// pwned password 'monkey123'
    "ok": true,
    "score": 0,
    "pwned": 56491
// stronger password 'wonderful waffles'
    "ok": true,
    "score": 3,
    "pwned": 0

By default, if pwned is greater than 0, then score will always be 0. You can override this behavior by settings "ALWAYS_RETURN_SCORE" to true in cloudflare.env

If RETURN_PW_METADATA is truthy, responses will also include a metadata key with the complete zxcvbn strength estimation result object.

Each response will also contain a x-worker-last-modified header with a timestamp indicating when the script was built and deployed.


Failure will return JSON to inform you that something's not ok and a message as to why.

  "ok": false,
  "message": "It went kaput 💩"

Good to Know

Send a GET request to act as a little health-check. Response 204 means you're good to go. Useful for testing CORS configuration 👍

Because Software


I am not affiliated with Cloudflare, Troy Hunt, Dropbox, haveibeenpwned, good software development in general, or any combination thereof.

Handling user passwords is no laughing matter, so handle them with care and respect.

Just like your own users, assume that I have no idea what I'm doing. This part is important, because I have no idea what I'm doing.

REVIEW THE SOURCE, and use at your own risk 🙈




Deploy a Cloudflare Worker to sanely score users' new passwords with zxcvbn AND check for matches against haveibeenpwned's 10+ billion breached accounts