node.js

const crypto = require('crypto')
const superagent = require('superagent')
const aws = require('aws-sdk')
const sns = new aws.SNS({
  apiVersion: '2010-03-31',
  region: 'ap-northeast-1'
});
exports.handler = async (event) => {
  const message = JSON.parse(event.body)
  const pemFile = await superagent.get(message.SigningCertURL)
  const pemContent = pemFile.body.toString('utf-8')
  const verify = crypto.createVerify('sha1WithRSAEncryption')
  const arr = ['Message', 'MessageId', 'Subject', 'Timestamp', 'TopicArn', 'Type']
  arr.forEach(key => {
    if (key in message) {
      verify.write(`${key}\n${message[key]}\n`)
    }
  })
  verify.end()
  const result = verify.verify(pemContent, message.Signature, 'base64')
  console.log(result) // trueなら署名検証OK
  const response = {
    statusCode: 200,
    body: JSON.stringify('Hello from Lambda!'),
  };
  return response;
};