Setting up SSO for two instances of Auth0

We are two SaaS startups using Auth0 in our respective applications independently. Since both our users are in separate custom domains of Auth0, we want to setup an SSO between both our applications. So that users of one app can seamlessly use the features of the other app.

Lets say we have App-A, App-B are the two SaaS applications. When user of App-A hits the Auth0 url of App-B, needs to get access to App-B pages.

How can we setup routing/SAML connection in App-B so that all App-A users get authenticated with the token generated by the Auth0 identity provider of App-A

We are very new to Auth0, feedback much appreciated