Saving credentials for subdomain in iOS keychain

Question

I have an iOS in SwiftUI and I have domain.com as well as subdomain.domain.com setup with the apple-app-site-association file. This is working so far and my app opens when these links are called.

In my app I sign up with the standard keychain heuristics and the TextField textContentType(.username) and textContentType(.newPassword) of iOS that detects username and password and saves them into the keychain. This is all working so far, however I make my API call to subdomain.domain.com but iOS saves the keychain item under domain.com.

My apple-app-site-association file for domain.com looks like this:

{
  "applinks": {
    "apps": [],
    "details": [
      {
        "appID": "XXXXXXX.com.domain.app",
        "paths": [
          "/app/*"
        ]
      }
    ]
  }
}

My apple-app-site-association file for subdomain.domain.com looks like this:

{
  "applinks": {
    "apps": [],
    "details": [
      {
        "appID": "XXXXXXX.com.domain.app",
        "paths": [
          "*"
        ]
      }
    ]
  },
  "webcredentials": {
    "apps": [
      "XXXXXXX.com.domain.app"
    ]
  }
}

My Associate Domain entitlement in the app looks like this:

applinks:domain.com
applinks:subdomain.domain.com
webcredentials:subdomain.domain.com

How can I tell iOS to save the item under subdomain.domain.com?