Origin Response lambda@edge function for setting a cookie

cf-origin-switch_origin-response.js

'use strict';

const AWS = require('aws-sdk');
const ssm = new AWS.SSM({ region: 'eu-central-1' });

const SOURCE_COOKIE_NAME = 'myapp-origin';
const LATEST_ORIGIN_GIT_HASH = 'myapp_latest-origin-git-hash';

exports.handler = async event => {
    console.group('[INFO] lambda@edge Origin Response')
    const request = event.Records[0].cf.request;
    const response = event.Records[0].cf.response;

    const latestOriginHash = await ssm.getParameter({
        Name: LATEST_ORIGIN_GIT_HASH,
        WithDecryption: false,
    }).promise();

    const hash = latestOriginHash.Parameter.Value;
    console.log(`Latest git hash is ${hash}`);

    if (request.headers.cookie) {
        for (let i = 0; i < request.headers.cookie.length; i++) {
            if (request.headers.cookie[i].value.indexOf(SOURCE_COOKIE_NAME) >= 0) {
                console.log(`Source cookie found. ${request.headers.cookie[i].value}`);
                setCookie(response, hash);
            }
        }
    } else {
        console.log('No Source cookie found');
    }

    console.log(request.headers['cache-control'])
    console.groupEnd()
  
    return response;
};

// Add set-cookie header (including path)
const setCookie = function (response, cookieValue) {
    const cookiePath = '/';
    const cookie = `${SOURCE_COOKIE_NAME}=${cookieValue}; Path=${cookiePath}; SameSite=None; Secure;`;

    console.log(`Setting cookie ${cookie}`);

    response.headers['set-cookie'] = [{ key: 'Set-Cookie', value: cookie }];
};