Connecting through zero trust access proxies

Steps to reproduce

1. Place Nextcloud server address behind zero trust access proxy like Cloudflare Access, Pomerium, etc.
2. Attempt to setup account in iOS app; enter serve address normally, e.g., https://my.nextcloud.org

Expected behaviour

The iOS app shows the web-based authentication page for the access proxy, and after passing through that access proxy, it caches the authentication tokens, and the Nextcloud authentication pops up (or does not if it's configured for SSO). By caching the authentication tokens, normal usage of the app is allowed until they expire. When they expire, the app throws up the access proxy authentication page to refresh the access tokens.

Actual behaviour

After entering the server address and tapping log in, the iOS app produces this error "Connection error 200: Transfer stopped."

Reasoning or why should it be changed/implemented?

This makes a zero trust configuration impossible if wanting to allow usage of the iOS app by the server's users. This will be increasingly important for enterprise users.

Environment data

Nextcloud iOS app version: 3.3.1.1

No files or tests are named. Reproduce the account setup with a Nextcloud server behind Cloudflare Access or Pomerium, then trace the iOS login flow from server-address entry. Done means the proxy authentication page appears, authentication tokens are retained for normal use, and expired tokens can be refreshed through the proxy.