You do need an authorized person to solemize, though as it happens, that can be almost anyone you want, because of a special program that allows anyone of legal age and of clean record to be licensed as "Justice for A Day." There's a bit more than the ceremony to it -- paperwork and such, but if you have a person who isn't otherwise authorized (clergy, JoTP, ship Captain, etc), they can write to city hall for that one day authorization.