Checking status of jure matrimoni

According to a recent post on the Italian Citizenship Message Board, this is the process for checking the status of a jure matrimoni application:

First you register here: https://cittadinanza.interno.it/sicitt/registrazione_user

After registering, login again (https://cittadinanza.interno.it/sicitt/index2.jsp) and add your husband file with the K number and the date you have submitted in consulate.

Now I just need to figure out what the "K number" is.