Hook that can be used to check for users in a configuration table.
Class TableCheckUser from \
Hook(( "check_user"))
This hook engages with the "check_user" function, and receives a user/password pair to be authenticated.
Authentication happens by checking a dictionary set in the configuration under the user key. Each user key must be associated with an entity of class User.
Passwords may be hashed through an arbitrary algorithm. In that case, the configuration must include a hash key pointing to the function used to obfuscate the passwords.
Eventually, a dflt configuration key can contain a default user entity that is returned if the password is not matched.