Would this be solved by providing the client with a (frequently rotated) public key to encrypt the password field specifically before submitting to the server, so that the only place it can be decrypted and stored is the authentication service at the very end of its journey through the network?
A new public key per password-mutating session is quite an interesting idea.
It does have some challenges in introducing a read-before-write to fetch the session key at the start of the session, but given the relatively low call volume of such flows that might be a small price to pay to simplify security audits and de-risk changes to any service in the call chain.
Unfortunately my understanding is that it’s trivial to implement unsoundly but it’s also not something for which there are an abundance of good implementations across languages.
It’s been awhile since I’ve looked though so maybe there is a newer, less radioactive approach. But yes, never actually sending the authenticator itself (and doing so in a way that the proof is valid only once) would stop this sort of thing cold.
