Agreed! Somebody else made exactly the same request while I was at the Hackathon a couple of weeks ago. I'd like feedback on several potential - possibly backward-incompatible - changes:

There are multiple steps that would be necessary for this to be achieved. First, the remote identity provider would need to support some API that would allow password changes. Often password changes are done through another mechanism (e.g. changing a Windows domain password or changing a password in a Google profile) with no API support provided. But, assuming that such a mechanism is available, a good place to start investigation would be to trace the flow from Special:ChangePassword. You would likely need to implement another special page to use instead of Special:ChangePassword. (Special:ChangePassword really should be disabled by PluggableAuth if local login is disabled, because currently it just gives a non-user-friendly error message in that case.) It does seem likely that an implementation would be needed for providerChangeAuthenticationData, but that implementation would be dictated by support in the plugin, since not all plugins would support remote password change. So, perhaps that would be a hook point. You'd need to figure out what information you'd need in the plugin to determine what the interface at the hook point would need to be. And, since many plugins would not support password changes, PluggableAuth should handle that case in a user-friendly manner.

(I guess I could/should have done that with my volunteer hat on rather than my WMF hat on . . .)

Ah, composer. @Kghbln, thanks for trying! @Yaron_Koren, will there be a new minor release of Page Forms at any point soon?

I created https://sandbox.semantic-mediawiki.org/wiki/Form:TestWikiEditor that you should be able to test against by visiting https://sandbox.semantic-mediawiki.org/wiki/Special:FormEdit/TestWikiEditor/testpage. However, the version of PageForms installed there is incompatible with the version of WikiEditor installed there (0.5.2 (aea465f)), since the function WikiEditor.isSupported() was removed. I have submitted https://gerrit.wikimedia.org/r/c/mediawiki/extensions/PageForms/+/476524 to fix PageForms to work with newer WikiEditor versions in a backward compatible manner. Once @Yaron_Koren is able to review/merge that patch and @Kghbln is able to update the sandbox wiki, this should be testable there.

Actually, my past experience was for properties, not categories, but I think the same logic may apply.