Clojurians Log v2

Spec question - say I have a fn signature like this: (defn foo [a b & {:keys [c d]}]). So a and b should be integers and c and d should be strings. But of course, c and d are optional, and the callsite can have two forms: either (foo a b :c "bar" :d "baz") or (foo a b {:c "bar" :d "baz"}). How can I write the :args part of (fdef foo :args ...) ?