That's going to be done under a court order -- probably MULTIPLE court orders -- from a judge presiding over the cases Mueller's team of misfit lawyers are prosecuting.
The defendants in these cases have the right to see this evidence, and to potentially call this source as a witness.
It's actually intriguing to see how this is all playing out. Devin Nunes and his committee aren't doing this to reveal the source. They're doing this to inform the defense attorneys in those various cases that this source exists.
“...doing this to inform the defense attorneys...”
Fascinating! theory. Interrogatories and Discovery next.