Sorry but that’s just wrong. The biggest auth systems in the world (Google, Amazon, Microsoft) do not rely on OAuth2 for internal services. Isolating auth into a central service and acquiring user consent as a third party, which very literally is the only purpose of OAuth2, are two very different things. Saying that you need a third party delegation tool to „scale“ an auth system is like saying that you need a good combustion engine to build an electric car.