Require either of multiple related keys with humanized error message

mailli-require-either.clj

(require '[malli.core :as m])
(require '[malli.error :as me])
(require '[malli.util :as mu])

(defn require-either [m ks]
  [:and
   (mu/optional-keys m ks)
   [:fn
    {:error/message (str "Must contain either of " ks)}
    `(fn [x#] (some x# ~ks))]])

(def Conf
  [:map
   [:name string?]
   [:password {:description "etc"} string?]
   [:fingerprint {:optional true} int?]
   [:retinal-scan any?]])

(-> Conf
    (require-either [:password :fingerprint :retinal-scan])
    (m/explain {:name "example"})
    (me/humanize))
=> #:malli{:error ["Must contain either of [:password :fingerprint :retinal-scan]"]}