Lambda@Edge to rewrite Host: header in Cloudfront based on client IP address

gistfile1.txt

// https://gist.github.com/prenagha/886c44526c7e9b1bc9e904900687f6b0
// https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-examples.html
// https://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/lambda-edge-permissions.html

'use strict';

exports.handler = (event, context, callback) => {
  let request = event.Records[0].cf.request;
  if (request['clientIp'].match(/^[456]/)) {
    request.headers['x-client-ip-match'] = [{'key': 'X-Client-IP-Match', 'value': 'true'}];
    request.headers['host'] = [{'key': 'Host', 'value': 'www2.zahna.com'}];
  } else {
    request.headers['x-client-ip-match'] = [{'key': 'X-Client-IP-Match', 'value': 'false'}];
    request.headers['host'] = [{'key': 'Host', 'value': 'www.zahna.com'}];
  }
  request.headers['x-client-ip'] = [{'key': 'X-Client-IP', 'value': request['clientIp']}];
  callback(null, request);
};