def fetch_auth_id!(barcode, library_symbol)
      auth = Authentication.new(barcode, library_symbol)
      # use the same HTTPClient so we use the same HTTP connection, perhaps
      # slightly more performance worth a shot. 
      auth.http_client = http_client
      self.auth_id = auth.get_auth_id
    end
def fetch_auth_id!(barcode, library_symbol)
      auth = Authentication.new(barcode, library_symbol)
      # use the same HTTPClient so we use the same HTTP connection, perhaps
      # slightly more performance worth a shot. 
      auth.http_client = http_client
      self.auth_id = auth.get_auth_id
    end
Fetches new authID, stores it in self.auth_id, overwriting
 any previous value there. Will raise BorrowDirect::Error if no auth
 could be fetched.

 returns auth_id too.