Cookies from root domain not accepted

[raycarter]

Hi, I'm trying to build an app with Ionic Capacitor and have now a problem with cookies. I think this is a trivial problem by building a Capacitor app with cookies. So I ask for help here. You are here all Capacitor experts ;)

The app should use cookie for user to login. Let's say the server is example.com and the app in Capacitor WebView is hosted under myapp.example.com (by changing 'server --> hostname' in capacitor.config.json).
The problem is, when I fired a xhr-request from the app to the server, the Set-Cookie header in the response is not accepted. Here is an example of request and response:

Request:

Host: example.com
Origin: https://myapp.example.com
Referer: https://myapp.example.com/
Content-Type: application/json

Response:

Access-Control-Allow-Methods: GET, POST, DELETE, PUT, OPTIONS, HEAD
Access-Control-Allow-Origin: *
Set-Cookie: a=something; Domain=example.com; Path=/; HttpOnly; Secure
X-Frame-Options: sameorigin

How can I get the cookie accepted in WebView? Which headers should actually be set (Access-Control-Allow-*, Set-Cookie, etc.)? Is there any other special settings in the xhr-request what I am missing?