(defn add-identity
  "Add an identity to the agent."
  ([]
     (add-identity *ssh-agent* (default-identity) nil))
  ([private-key]
     (add-identity *ssh-agent* private-key nil))
  ([agent private-key]
     (if (ssh-agent? agent)
       (add-identity agent private-key nil)
       (add-identity *ssh-agent* agent private-key)))
  ([#^JSch agent private-key #^String passphrase]
     (.addIdentity
      agent
      (if (instance? Identity private-key)
        private-key
        (file-path private-key))
      (and passphrase (.getBytes passphrase))))
  ([#^JSch agent #^String name #^bytes private-key #^bytes public-key
    #^bytes passphrase]
     (.addIdentity
      agent name private-key public-key passphrase)))