I just read the opinion in its entirety, including some well deserved flaming dissent, and I see nothing that requires that anyone provide ID. The case concerns permissible investigations under the 4th amendment. The only mention of identification is when the court cites United States v. Brignoni-Ponce: "The stop does intrude to a limited extent on motorists' right to 'free passage without interruption,' and arguably on their right to personal security. But it involves only a brief detention of travelers during which ‘(a)ll that is required of the vehicle's occupants is a response to a brief question or two and possibly the production of a document evidencing a right to be in the United States.’” This quote arises in the Government's brief in Brignoni, they are not the words of the court. I wouldn't venture to characterize this as setting forth the requirement to ID in any way, just a statement of what is requested by the officers and what is required for the stop to go smoothly. To some degree it would also depend on the wording of the statute, whether proof of citizenship is an affirmative defense or whether lack of citizenship is an element of the crime under investigation.
The way I read the opinion, the words, "(a)ll that is required..." are quoted inline and, therefore, become a part of the line of reasoning of the justice writing the opinion. He is merely attributing the source of the words he is incorporating into the opinion.
If such a short questioning and production of ID has been ruled not a violation of the 4A at checkpoints
away from the border, surely brief questioning and production of ID would also be allowable
at the border.
That being said, IMO, checkpoints
away from the border are intrusions that the Founders would have found objectionable. Also IMO, the Founders would not have believed that anyone could enter the nation that they formed without question, and would have held that the nation had the authority to reject the entry by anyone other than a citizen (or whatever you prefer that status be called at that time in history) for any reason.
They, of course, did not have border checkpoints at the time. (Consider the size of the "border" relative to the size of the nation at the time and its western fuzziness.) Such questioning of a foreigner's presence (and right to be present) would likely have happened locally. Also, of course, having ID was not routine at the time.
However, I have no doubt that, viewing the circumstances today, whereby we have routine ID and there are millions trying to enter and succeeding at entering the nation against her laws regarding entry, the Founders would not have blinked twice at the notion of a few questions as to why a person thought he should be allowed to enter the nation nor at the production of such routine ID
at the now well-defined border. Even without probable cause that the person was not being forthright, they surely would have thought that such a stop at the border was not unreasonable and, therefore, not a violation of the 4A. With probable cause, of course, more in-depth search and seizure would be called for.
Are border patrol agents allowed to ask you a few questions and demand ID at the border? This opinion is silent on that issue. However, since it holds that such stops are lawful at fixed places
away from the border, surely such stops would be lawful
at the border.