httpOnly cookies in cross-domain requests not being sent - cookies

Question

I'm really really sorry for asking yet another CORS question but I'm stuck and I can't understand why.
I have any API that, on login, responds with a Set-Cookie header which sets a cookie with my user info. This is what that response looks like:
Response from api.somesite.com
Access-Control-Allow-Credentials: true
Connection: keep-alive
Content-Length: 183
Content-Type: text/html; charset=utf-8
Date: Mon, 19 Apr 2021 19:55:02 GMT
Set-Cookie: socialAccesstoken=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6Ijk5MDk3NzQzNjkxNjU1MTY4MCIsInVzZXJuYW1lIjoiY3JlYXRpdmlpaSIsImRpc3BsYXlOYW1lIjoiTGVvIDjvuI_ig6MiLCJ1cmwiOiJodHRwczovL3QuY28vWjNBM01xaFBDbiIsInBob3RvIjoiaHR0cHM6Ly9wYnMudHdpbWcuY29tL3Byb2ZpbGVfaW1hZ2VzLzEzNzExMzQ3MjY0NzI0MTMxODYvZ0Q5Sk5lVU1fbm9ybWFsLmpwZyIsInByb3ZpZGVyIjoidHdpdHRlciIsImlhdCI6MTYxODg2MjEwMiwiZXhwIjoxNzA1MjYyMTAyfQ.Q7yWf-ywoZ-rWOhYseKTt_0V2_AlEMQ-cCL2rlRNm_U; Max-Age=86400; Path=/; Expires=Tue, 20 Apr 2021 19:55:02 GMT; HttpOnly
Vary: Origin
X-Powered-By: Express
The Cookie is set successfully and I can view it in the Application tab for api.somesite.com.
I then try to make a request from a page on the same domain:
Request from somesite.com to api.somesite.com
Response
HTTP/1.1 200 OK
X-Powered-By: Express
Access-Control-Allow-Origin: http://somesite.com:8000
Vary: Origin
Access-Control-Allow-Credentials: true
Token-Expired: true
Content-Type: application/json; charset=utf-8
Content-Length: 196
ETag: W/"c4-HQkmHNLuibgvd4gvz0JqjTLKjFU"
Date: Mon, 19 Apr 2021 19:59:18 GMT
Connection: keep-alive
Request
Host: api.somesite.com:3000
Connection: keep-alive
Content-Length: 143
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.128 Safari/537.36
content-type: application/json
Accept: */*
Origin: http://somesite.com:8000
Referer: http://somesite.com:8000/
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,en-US;q=0.9,en;q=0.8
Cookie: socialAccesstoken=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6Ijk5MDk3NzQzNjkxNjU1MTY4MCIsInVzZXJuYW1lIjoiY3JlYXRpdmlpaSIsImRpc3BsYXlOYW1lIjoiTGVvIDjvuI_ig6MiLCJ1cmwiOiJodHRwczovL3QuY28vWjNBM01xaFBDbiIsInBob3RvIjoiaHR0cHM6Ly9wYnMudHdpbWcuY29tL3Byb2ZpbGVfaW1hZ2VzLzEzNzExMzQ3MjY0NzI0MTMxODYvZ0Q5Sk5lVU1fbm9ybWFsLmpwZyIsInByb3ZpZGVyIjoidHdpdHRlciIsImlhdCI6MTYxODg2MTQ2MiwiZXhwIjoxNzA1MjYxNDYyfQ.BpmQzWWYuBHLQQh6VpatflBsQUv2A0ahLqt1UgYOq8Q
As you can see the cookie is sent correctly.
But then if I switch my api to api.differentsite.com and make the same requests:
Response from api.differentsite.com
HTTP/1.1 200 OK
X-Powered-By: Express
Vary: Origin
Access-Control-Allow-Credentials: true
Set-Cookie: socialAccesstoken=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6Ijk5MDk3NzQzNjkxNjU1MTY4MCIsInVzZXJuYW1lIjoiY3JlYXRpdmlpaSIsImRpc3BsYXlOYW1lIjoiTGVvIDjvuI_ig6MiLCJ1cmwiOiJodHRwczovL3QuY28vWjNBM01xaFBDbiIsInBob3RvIjoiaHR0cHM6Ly9wYnMudHdpbWcuY29tL3Byb2ZpbGVfaW1hZ2VzLzEzNzExMzQ3MjY0NzI0MTMxODYvZ0Q5Sk5lVU1fbm9ybWFsLmpwZyIsInByb3ZpZGVyIjoidHdpdHRlciIsImlhdCI6MTYxODg2MjYzMSwiZXhwIjoxNzA1MjYyNjMxfQ.MvOLarBw_Mz-h26WvOrOqyE0IaDQEnIqp2xLUiFqAZQ; Max-Age=86400; Path=/; Expires=Tue, 20 Apr 2021 20:03:51 GMT; HttpOnly
Content-Type: text/html; charset=utf-8
Content-Length: 183
Date: Mon, 19 Apr 2021 20:03:51 GMT
Connection: keep-alive
(the cookie is set correctly at api.differentsite.com:3000 according to the Application tab in Chrome)
And then I try to make a request from somesite.com:
Response
HTTP/1.1 200 OK
X-Powered-By: Express
Access-Control-Allow-Origin: http://somesite.com:8000
Vary: Origin
Access-Control-Allow-Credentials: true
Content-Type: application/json; charset=utf-8
Content-Length: 147
ETag: W/"93-2hkHY0W/lJkUQBK+JwrKp/OTCro"
Date: Mon, 19 Apr 2021 20:03:26 GMT
Connection: keep-alive
Request
POST /api HTTP/1.1
Host: api.differentsite.com:3000
Connection: keep-alive
Content-Length: 143
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/89.0.4389.128 Safari/537.36
content-type: application/json
Accept: */*
Origin: http://somesite.com:8000
Referer: http://somesite.com:8000/
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,en-US;q=0.9,en;q=0.8
There's no cookie sent, so authorisation fails.
Why is this happening? This should work, no?
My request looks like this:
const headers = new Headers();
headers.append("Content-Type", "application/json");
const result = await fetch(endpoint!, {
method: "POST",
headers,
body,
redirect: "follow",
credentials: "include",
}).then((response) => response.json());
I've checked over and over again and I'm certain these settings are correct.
I've followed the advice on this question but they didn't work. I'm unsure what Access-Control-Allow-Headers I should add on my request.

Answer 1

Looks like a night's sleep was all I needed.
The problem was caused by my cookies missing the correct settings. For httpOnly cookies to be sent in cross-domain requests they need to have:
same-site set to none
secure set to true
So I made sure these two values were set on cookies when in production:
sameSite: process.env.NODE_ENV === 'production' ? 'none' : 'lax',
secure: process.env.NODE_ENV === 'production' ? true : false,
And it started working.
EDIT:
While this is the correct answer, it seems that Safari now blocks third party cookies by default, meaning no cookies will be sent if the client is safari. This can be deactivated in the settings, but it's on by default.