(find-header resp header-name)
Looks up a header in a Ring response (or request) case insensitively,
returning the header map entry, or nil if not present.
Source
(defn find-header
"Looks up a header in a Ring response (or request) case insensitively,
returning the header map entry, or nil if not present."
{:added "1.4"}
[resp ^String header-name]
(->> (:headers resp)
(filter #(.equalsIgnoreCase header-name (key %)))
(first)))