code: def _auth_key(nonce, username, password):
      
      digest = _password_digest(username, password)
      md5hash = hashlib.md5()
      data = "%s%s%s" % (nonce, username, digest)
      md5hash.update(data.encode('utf-8'))
      return _unicode(md5hash.hexdigest())
docs: Get an auth key to use for authentication.