I think the zero-knowledge proof bit is how some password managers authenticate the users to their system. 1Password for example, uses the secure remote password protocol: https://en.wikipedia.org/wiki/Secure_Remote_Password_protoco... , that is mentioned in https://blog.1password.com/1password-is-layerup-ed-with-mode... as a zero-knowledge password authenticated key agreement when you login to fetch the blob of encrypted password data from 1password.