SuperTokens is an open source authentication solution offering features like: Different types of login: Email / password, Passwordless (OTP or Magic link based).

SuperTokens.com

Hey everyone. I'm trying to build something simular to Shopify auth architecture (Main portal + subportals with it's own users). I'm thinking about creating a dedicated userpool and auth server for the main portal and one more for sub-portals with modified identifier (ex: email+origin). Is there any way to silently create user in a sub-portals pool once there is a new user in the main userpool. So there will be no need for the sub-portal creator to sign up once again

The way you can do this is by making both the portals connect to the same supertokens core - so they share the same user pool.