I am trying to find a book, or poem in which a character has clothing that hides their true identity.

There are many books about Deborah Sampson. Sampson was a twenty-three year old woman who managed to conceal her gender in order to fight in the Continental Army during the Revolutionary War. She enlisted using the name Robert Shurtliff and dressed as male soldier in order to live and fight alongside the soldiers for over a year. Her identity was revealed after she became ill, and was treated in an army hospital. Masquerade: The Life and Times of Deborah Sampson, Continental Soldier by Alfred F. Youngtells the story of Sampson’s experiences, and attempts to dispel some of the hyperbole that surrounds her story. Another book that tells the story of Deborah Sampson is Soldier's Secret: The Story of Deborah Sampson by Sheila Solomon Klass. Later in life, Sampson spent time lecturing about her experiences.