Carefully remove the rind from lemon and orange using a vegetable peeler, making sure to avoid the white pith just beneath the rind. Cut citrus rind into 1- x 1/4-inch-thick strips. Combine the rind strips, cider, and remaining ingredients in a Dutch oven. Bring the mixture to a simmer over medium heat, and cook until reduced to 4 cups (about 30 minutes). Strain the mixture through a sieve over a bowl, discarding solids.