[BUG] in sample: LinkedIn Auth __session cookie does not persist when function is called by popup.html

### Which sample has a bug?

LinkedIn Auth

### How to reproduce the issue

Use popup.html and cloud functions as expected, however, due to node-linkedin deprecation, use axios to query for profile data. I would be willing to submit this for a PR once this bug is figured out.

**Steps to set up and reproduce**

Follow LinkedIn sign in flow, redirect function -> token function, etc.

### Debug output

req.cookies.__session returns null. However, if the token function is called manually (i.e., console.log popup.html's script.src and following the link), the __session cookie is there.

**Errors in the
[console logs](https://console.firebase.google.com/project/_/functions/logs?search=&severity=DEBUG)**

**Screenshots**
Cookie in redirect
Cookie in token function when called by popup
Cookie in token function when called manually

### Expected behavior

Cookie is null

### Actual behavior

Cookie persists