Adding a Shared Yahoo Calendar

My son shared his Yahoo calander with me and my wife.

My wife and I both have iPhones. She has the old version 4.2.8 and her phone setup with the shared yahoo calander with one click.

When I click on the email invitation send from my son's yahoo calander, I get a strange pop up telling me I need verification and asks for a username and password.

Every one I put in does not work! Does anyone know which username and password is being requested?