Web App Separate Isolated Session

johnjansen Thanks John, fully aware of the advantage of that. I tried to keep my initial post fairly concise. I'll stick to "web app" here as this is mostly about apps that people install from a website. e.g. they go to http://www.contoso.com, and then hit the '...' and 'Apps' -> "Install", regardless if the site is a standard webpage, or a proper PWA (with manifest, etc.).

In the case where an app is installed from having already visited the website, I could foresee keeping 'signed-in ness' and a consistent experience for devs, that same-site cookies could be kept, and all others discarded (this may still break SSO); with an option to start a fresh session for privacy focused users.

Personally, even if the user is required to sign-in again, I wouldn't expect that it would cause excessive friction/bounce rate. Even a notification "For your privacy, we keep this new App separate to your other browsing - so you'll have to sign in again".

As you indicated, A/B is the way to go.