webRequest listener doesn't see headers like 'cookie', 'referer', 'origin'

Question

We wrote a Chrome-extension that, using the onBeforeSendHeaders event, adds a cookie to each web request:

chrome.webRequest.onBeforeSendHeaders.addListener         


        

Answer 1

According to this https://developer.chrome.com/extensions/webRequest

• Starting from Chrome 72, the following request headers are not provided and cannot be modified or removed without specifying 'extraHeaders' in opt_extraInfoSpec:

  • Accept-Language
  • Accept-Encoding
  • Referer
  • Cookie

• since Chrome 79:

  • Origin
  • CORS preflight requests

Response headers for other listeners like onHeadersReceived:

• since Chrome 72:
  • Set-Cookie
  • any header you want to modify before CORB is applied
• since Chrome 79:
  • CORS preflight responses

So you should add "extraHeaders" to the third parameter of the webRequest listener and it should be ["blocking", "requestHeaders", "extraHeaders"] for your example.

Note that it won't run in old pre-72 Chrome, which doesn't know about extraHeaders, so you can use the following trick to have a universally compatible listener:

chrome.webRequest.onBeforeSendHeaders.addListener(
  addCookie,
  {urls: ["<all_urls>"]},
  ["blocking", "requestHeaders",
   chrome.webRequest.OnBeforeSendHeadersOptions.EXTRA_HEADERS].filter(Boolean)]
);