In a medium saucepan, heat 1/2 cup water with the orange zest, orange juice, sugar and salt over medium-high heat, stirring until the sugar dissolves, 2 to 3 minutes. Stir in the cranberries and bring to a boil. Reduce the heat and simmer until the cranberries burst and the sauce has thickened slightly, about 7 minutes. Sweeten with more sugar, if desired. Let the sauce cool to room temperature before serving.