The President got that approval from Congress in 1863.
As for the South,
If the South was so concerned about Constitutional rights, let's look at how the Confederacy dealt with constitutional issues on her own soil. Freedom of the press was always tenuous -- beginning with the Secession convention in Charleston. At that time Robert Barnacle Rhea advised the editor of the New York Evening Post not to send a reporter: "No agent or representative of the Evening Post would be safe in coming here . . . He would come with his life in his hand, and would probably be hung." On April 14, 1861, even before President Lincoln called out troops to suppress the rebellion, the Confederate States arrested a journalist, Lawrence Matthews, for his reporting in Pensacola, Florida. And throughout the Civil War, journalists were required to obtain travel passes. And the Confederacy's President, Jefferson Davis, had no philosophical turmoil suspending the writ of habeas corpus and jailing Southerners without specified cause. In fact, it was only 15 years after the Civil War, when Jefferson began writing The Rise and Fall of the Confederate Government, that he began to construct the myth of constitutionalism.
http://www.chicora.org/myth_conceptions.htm
The Confederate Congress authorized Davis to suspend habeas corpus for specified time periods. Lincoln on the other hand suspended it on his own in 1861, for which the US Congress later had to indemnify him. If Lincoln had the power to suspend habeas corpus, as some Northern posters argue, why did the US Congress authorize Lincoln to suspend it in 1863?
Lincoln invaded Maryland and gave orders to General Scott to use force and suspend the habeas corpus. No mention of Congress.