Can Multipass facilitate automatic login for both web app and online store?

[Anandds]

Hi: I am looking at the following scenarios:

1. User visits my web app and logs in using their existing credentials. User should be logged into myshopify store if they decide to visit it.

2. User visits myshopify store, logs in with shopify credentials and decide to navigate to my web app. User should be automatically logged into my web app.

3. User visits myshopify store and attempts to log in with web app credentials. User should be able to do so. 

4. User visits my web app and attempts to log in with shopify credentials. User should be able to do so.

I know 1 and 2 are possible with multipass. Is 3 and/or 4 even possible? If so, how?