iOS and Keychain - how to get known passwords in Safari to be used in a related app

Solution 1:

Yes, it is technically possibly for apps to behave that way - but only if the developer of the app has arranged for it. If the app does not support autofilling passwords that way, it is not possible for users to change that.

For developers, it is very simple to support this feature. The developer primarily has to list their domains (such as my-web-site.com) in the Info.plist file in the app, and then add a single JSON-file named apple-app-site-associate to the web server on that domain.

The details for developers are specified here:

https://developer.apple.com/documentation/security/password_autofill/about_the_password_autofill_workflow

and here:

https://developer.apple.com/documentation/xcode/supporting-associated-domains