Next.js not persisting cookies - cookies

Question

I have a server-side rendered Next.js/express app that communicates with a Django API (cross-origin). I login a user like so:
const response = await fetch('localhost:8000/sign-in', {
method: 'POST',
credentials: 'include',
body: JSON.stringify({ email, password }),
headers: { 'Content-Type': 'application/json' },
});
const result = await response.json();
if (response.status === 200) {
Router.push('/account');
}
Django successfully logs in the user and returns set-cookie headers for the csrftoken and sessionid cookies, however, when I navigate to a different page (like in the above code when I Router.push), the cookies don't persist.
I assume this has something to do with server-side vs. client-side, but when cookies are set in the browser I expect them to persist regardless.
How can I get these cookies, once set, to persist across all pages on the client side?

Answer 1

It turns out that set-cookie is the old way of doing things. It's controlled by the browser, so it's obfuscated.
I ended up sending the csrftoken and sessionid back to the client in the JSON body, and saving them to localStorage using localStorage.setItem('sessionid', 'theSessionId') and localStorage.setItem('csrftoken', 'theCsrftoken').
Then when I need to make an authenticated request, I include them in the fetch headers:
const response = await fetch(`${API_HOST}/logout`, {
method: 'POST',
headers: {
'X-CSRFToken': localStorage.getItem('csrftoken'),
sessionid: localStorage.getItem('sessionid'),
},
});