Keith Urban is about to sign up with the “American Idol” judging panel, Page Six has exclusively learned. The country star and husband of Nicole Kidman has agreed to join the Fox show as a judge, and finishing touches are being put on his contract. A source tells us, “Keith will bring a huge country following to the show, and bring a different viewpoint to the panel.” We’re also told that while Mariah Carey is set, negotiations with Nicky Minaj continue, but the deal is “90 percent done,” with a sticking point being her deal with Pepsi, because the show is sponsored by Coca-Cola. We are told, “Producers really want a fourth judge,” and will probably keep Randy Jackson, offering him a new contract.