Feel free to challenge it.
OLC released this in 2005, "Whether the President May Sign a Bill by Directing That His Signature Be Affixed to It." Bottom line up front, it starts with "The President need not personally perform the physical act of affixing his signature to a bill he approves and decides to sign in order for the bill to become law. Rather, the President may sign a bill within the meaning of Article I, Section 7 by directing a subordinate to affix the President’s signature to such a bill, for example by autopen."