Cookies not being stored with Fetch
You encountered an interesting case. The thing is that behavior of fetch function is different rather than XMLHttpRequest. To work with cookies in fetch you should explicitly provide credentials option.
fetch('http://127.0.0.1:4000/authorize-cookie', { method: 'POST', body: JSON.stringify({token: token}), credentials: 'same-origin', // <- this is mandatory to deal with cookies})According to the article on MDN
Credentials: The request credentials you want to use for the request: omit, same-origin, or include. To automatically send cookies for the current domain, this option must be provided.