I have been reading about Zero Knowledge Proof (ZKP) protocols for a while now. Among the applications I have seen the most is authentication (https://ethereum.org/en/zero-knowledge-proofs/#authentication). But in practice it is not used; why?
I have also been looking for why these protocols are not used in authentication systems or why they are not used by identity providers (such as Google accounts, Facebook, Microsoft, etc.).
One application I can think of is an identity provider where you don't have to register and log in in the conventional way, but uses ZKP. Would this be viable?