Background chrome script to download cookies for a domain

background.js

const DOMAIN = 'calendar.google.com'
const FILENAME = 'gcal-cookies.txt'

/** --------
    This background chrome extension script will download all cookies
    for a page into a file periodically when you visit, useful for if
    you can't generate your own API Access tokens or service accounts
    but want to use your logged in cookies to read from a service,
    e.g. google calendar

    Manifest
    {
      "name": "Cookie Exporter",
      "version": "1.0",
      "manifest_version": 2,
      "permissions":[
        "tabs",
        "downloads",
        "cookies",
        "*://*.google.com/*"
      ],
      "background": {
        "scripts": ["background.js"]
      }
    }
*/

let lastDownload = 0

chrome.tabs.onHighlighted.addListener(async _ => {
  let queryOptions = { active: true, currentWindow: true }
  chrome.tabs.query(queryOptions, ([tab]) => {
    if (tab.url.includes(DOMAIN)) {
      // Check to see if we've downloaded cookies recently
      const timeDiffHours = (new Date() - lastDownload) / 1000 / 60 / 60
      if (timeDiffHours < 12) {
        console.log(`Skipping download: ${Math.floor(timeDiffHours)}hrs since last download`)
        return
      }

      chrome.cookies.getAllCookieStores(stores => {
        let { id: storeId } = stores.find(s => s.tabIds.includes(tab.id)) || {}
        if (!storeId) return

        chrome.cookies.getAll({ storeId, url: tab.url }, (cookies) => {
          const cookieString = cookies
                .reduce((acc, it) => acc + `${it.name}=${it.value}; `, '')
          const cookieDataUri = encodeURI(`data:text/plain,${cookieString}`)

          chrome.downloads.download({
            url: cookieDataUri,
            filename: FILENAME,
            conflictAction: 'overwrite'
          }, () => {
            console.log(`Downloading cookies`)
            lastDownload = new Date()
          })
        })
      })
    }
  })
})