authz may be confusing to non USA English speakers. I wouldn't make the connection without it spelled out to me. Unfortunately I don't have a better suggestion because auths as short for authorisation is probably worse.
To me they look like the kind of abbreviations I'd only do when writing. I just say authentication or authorisation when reading them (out loud or in my own mind)
authn/authentication: user proves who they are, with username/password or otherwise
authz/authorization: based on who the user is, system determines what they are allowed to do, via group membership or otherwise