lambda-captcha

Generates captchas that can be verified decentrally.

Description

This is heavily inspired by svg-captcha, but written in TypeScript. It also allows you to pass the generated captcha expressions together with the user-supplied captcha solution, so you can verify the results independently. The captcha expressions are encrypted, so they are not machine readable.

Usage

Generating a captcha

const lambdaCaptcha = require('lambda-captcha')
const SECRET = process.env.CAPTCHA_SECRET

function generateCaptcha() {
  const captchaConfig = lambdaCaptcha.LambdaCaptchaConfigManager.default(SECRET)
  const captcha = lambdaCaptcha.create(captchaConfig)

  return {
    // The captcha SVG that you can display inside e.g. a form
    captchaSvg: captcha.captchaSvg,
    
    // This is the un-encrypted expression of the captcha.
    captchaExpression: captcha.expr,
    
    // This is the encrypted expression of the captcha.
    // Pass it along with your server side verification requests.
    encryptedCaptchaExpression: captcha.encryptedExpr
  }
}

Verifying a captcha

const lambdaCaptcha = require('lambda-captcha')
const SECRET = process.env.CAPTCHA_SECRET

function verify(encryptedCaptchaExpression, captchaSolution) {
  const captchaResult = lambdaCaptcha.verify(captchaExpression, captchaSolution, SECRET)
  return captchaResult // either true on success or false if the solution was wrong
}

Testing

npm run test

or

npm run tdd