What is the best practice for linking data to user models that are sourced from Identity Provider (e.g. Google, Facebook etc.)?

Imagine i got a web app that stores Games and Game Devices and users that own them. Normally the design would be having user linked to Games and Game Devices via many-to-many relationship etc. when all the entities are in same location. Therefore the foreign key would be the ID of the entity entry.

Now refactor the user out of the web app, so that identity is provided via an external source (e.g. Google, Facebook etc.), how would you demonstrate the relationship to the Games & Game Devices now that the User entity is external?

What is the best pracice to demonstrate this relationship? Should i be just plugging in the email/id that is provided by the external identity provider?

Kind of confused as to how to approach this problem.