code: def calculate_hmac(cls, params):
          
          encoded_params = cls.__encoded_params_for_signature(params)
          # Generate the hex digest for the sorted parameters using the secret.
          return hmac.new(cls.secret.encode(), encoded_params.encode(), sha256).hexdigest()
docs: Calculate the HMAC of the given parameters in line with Shopify's rules for OAuth authentication.
          See http://docs.shopify.com/api/authentication/oauth#verification.