This would be standard operating procedure in any normal Presidency. Attorney General Eric Holder is the executive branch's chief legal officer, and Administrations of both parties typically ask OLC for advice on the parameters of presidential legal authority.
The Obama Administration has asked OLC for its legal opinions on such controversial national security questions as drone strikes and targeting U.S. citizens abroad. It was right do so even though the Constitution gives Presidents enormous authority on war powers and foreign policy.
But a Justice-OLC opinion is all the more necessary on domestic issues because the President's authority is far more limited. He is obliged to execute the laws that Congress writes. A President should always seek legal justification for controversial actions to ensure that he is on solid constitutional ground as well as to inspire public confidence in government.
Yet as far as we have seen, Mr. Obama sought no such legal justification in 2012 when he legalized hundreds of thousands of immigrants who were brought to the U.S. illegally as children. The only document we've found in justification is a letter from the Secretary of Homeland Security at the time, Janet Napolitano, to law enforcement agencies citing "the exercise of our prosecutorial discretion." Judging by recent White House leaks, that same flimsy argument will be the basis for legalizing millions more adults.'