They explain that rules of war have been in the constitution from the beginning. They are based on common law rules of war and rules of war passed by congress. They were ammended after the war of 1812 to include U.S. Citizens.
They were used extensively in the Civil War.
There is nothing new in how they are to be used.
Again, you should download the decision and read it. It is 17 pages and very enlightening. The decision was 8 to 0.
It is constitutional. Law enforcement cannot deal with preventing spies and sabatours. That is why the rules of war were passed by congress. It is a war issue not a law enforcement issue.