Universal Login & SSO between auth0 applications

Hello, I have a use case that is not working as I expected:

I have 3 Auth0 applications, they are all of SPA type. and each one has a different DB Connection and a different set of users, identified by their email address.

Application1

Application2

Application3

I want user1@mail.com to be able to switch to Application2 and Application3 seamlessly. However, once user1 is logged into Application1, and I try to switch to Application2, it doesn’t log in.

What is the best way to achieve that behavior?

My use case is an organization with several departments, each department is represented by an instance of the same SPA, under different subdomains dep1.mydomain.com and dep2.mydomain.com. Users that belong to the organization level, should be able to see what’s going on in the Departments. Departments are independent by definition, imagine branches of a dealership or locations of a restaurant chain.

Any help is appreciated.