Funny, but US law says only CONGRESS can authorize such action. The Pres does not have the authority.
Very nice of you to point out yet another illegal act by 0bama.
There are multiple potential sources of authority in U.S. law for military action. As commander in chief, the president derives authority to use military force in certain circumstances from Article II of the Constitution. Congressional authorizations for the use of military force allow the president to lead a military campaign consistent with the scope defined by Congress. The War Powers Resolution was an attempt to restore the original constitutional balance on war powers between the legislative and executive branches. But in practice, it has afforded the president greater latitude to use military force at the outset of a conflict.