I'll add some context in the hope of answering @Vlad's questions.
Currently, to fill a password from Apple's Passwords app in Orion...
- you need to have Orion Passwords switched on in Settings (which is non-intuitive if you're not wanting to use Orion's passwords, only Apple's
- you need to click in the password field which is not always even present on the log in screen (think Google's two step log in screens)
- you need to select
Passwords
- you get a Passwords box with every single login you have saved in it, instead of just the logins for the site you're on, and sometimes it's impossible to search for the item you need, ie: when the site you're logging into is the same domain as your email address - searching for that domain doesn't filter the list down at all
I don't know what happens after this, as I've never successfully managed to log in to anything in Orion with an Apple Passwords login.
As for how this should work, the iCloud Passwords extensions for Firefox and Chrome essentially make autofilling behave the same as Safari.
- you arrive on a log in screen and it automatically offers you the logins it has stored for this specific site
- click one and you're in
In terms of getting this working in Orion, there's an interesting thread on GitHub where the devs of the Firefox fork Zen have been trying to get the Firefox extension working in their browser.
At the very least, I'd imagine it's worth opening a conversation with Ricky Mondello at Apple about making this work in a way that's usable. https://github.com/apple/password-manager-resources