in reply to Štěpán Škorpil

I see. This seems to be what everyone expects. However it is backwards, it lets you use the XMPP server as an IdP for signing into XMPP without the client application seeing passwords.

There is however overlap with the SSO against an existing IdP use case and that is also possible, with different configuration, if with more friction due to how existing OAuth2 things tend require that application developers register their application ahead of time.