According to this issue hcaptcha is not fixed yet.
And I just read the dendrite github page. The federation and client-server API's are complete, but the AS API isn't and things like SSO aren't implemented.
[...] there are still some missing features (like SSO and Third-party ID APIs).
We are prioritising features that will benefit single-user homeservers first (e.g Receipts, E2E) rather than features that massive deployments may be interested in (OpenID, Guests, Admin APIs, AS API).