In a medium saucepan, combine the port, sugar, star anise, salt, and 1/2 cup water. Bring to a boil over medium-high heat, stirring to dissolve the sugar. As soon as the mixture reaches a boil, remove it from the heat, cover, and let stand for 20 minutes to infuse the star anise into the liquid. Meanwhile, pick through the cranberries for stems, rinse them well in a colander, and let drain.
Return the liquid to a boil over medium-high heat and add the cranberries. When the mixture again returns to a boil, lower the heat to a simmer and cook, occasionally stirring gently, until most of the berries have popped open and the sauce has thickened slightly, 8 to 10 minutes. Discard the star anise. Stir in the orange zest and let the sauce cool to room temperature. If not using the same day, refridgerate for up to a week (return the sauce to room temperature before serving).