The sourcing is "current and former administration and congressional officials". As with the New York Times article on the FISA Court's secret body of law, it's interesting to me that people are discussing this with the press. Are the current administration officials talking with permission?

In classified orders starting in the mid-2000s, the court accepted that "relevant" could be broadened to permit an entire database of records on millions of people, in contrast to a more conservative interpretation widely applied in criminal cases, in which only some of those records would likely be allowed, according to people familiar with the ruling....

Two senators on the Intelligence Committee, Ron Wyden (D., Ore.) and Mark Udall (D., Colo.), have argued repeatedly that there was a "secret interpretation" of the Patriot Act. The senators' offices tell the Journal that this new interpretation of the word "relevant" is what they meant.