Get Real-IP of a user in a separate request header with CloudFront <-> Lambda@Edge

CloudFront_real_ip.js

// Get Real-IP of a user in a separate request header with CloudFront <-> Lambda@Edge
'use strict';

exports.handler = (event, context, callback) => {
    const request = event.Records[0].cf.request;
    const headers = request.headers;

    headers['true-client-ip'] = [{
        key: 'True-Client-IP',
        value: request['clientIp']
    }];


    callback(null, request);
};