Calcuate HMAC signature. Substitute `algorithm` for other types. This worked for me for validating Facebook webhook payloads.

calculate-hmac-signature.clj

;; Make sure you import javax.crypto.Mac and javax.crypto.spec.SecretKeySpec

(defn get-signature
  [message secret]
  (let [algorithm "HmacSHA1"
        signing-key (SecretKeySpec. (.getBytes secret) algorithm)
        mac (doto
             (Mac/getInstance algorithm)
             (.init signing-key))
        bytes->hex-str #(apply str (for [b %] (format "%02x" b)))]
    (->> (.getBytes message)
         (.doFinal mac)
         bytes->hex-str)))