code: async def find_user(cls, config: Config, user: str) \
              -> Tuple[str, str]:
          
          with open(config.users_file, 'r') as users_file:
              for line in users_file:
                  this_user, user_dir, password = line.split(':', 2)
                  if user == this_user:
                      return password.rstrip('\r\n'), user_dir or user
          raise InvalidAuth()
docs: If the given user ID exists, return its expected password and
          mailbox path. Override this method to implement custom login logic.
  
          Args:
              config: The maildir config object.
              user: The expected user ID.
  
          Raises:
              InvalidAuth: The user ID was not valid.