def signature
      # Remove 'sha_sign' key from request params and concatenate all
      # key value pairs
      params = payload.to_h
        .reject { |key, value| key == :sha_sign }
        .reject { |key, value| value == '' || value == false }.sort
        .map { | key, value| "#{key}=#{value}#{passphrase}" }.join

      # Calculate SHA512 and upcase all letters, since Digistore will
      # also return upcased letters in the signature.
      Digest::SHA512.hexdigest(params).upcase
    end
def signature
      # Remove 'sha_sign' key from request params and concatenate all
      # key value pairs
      params = payload.to_h
        .reject { |key, value| key == :sha_sign }
        .reject { |key, value| value == '' || value == false }.sort
        .map { | key, value| "#{key}=#{value}#{passphrase}" }.join

      # Calculate SHA512 and upcase all letters, since Digistore will
      # also return upcased letters in the signature.
      Digest::SHA512.hexdigest(params).upcase
    end
Initialize the notification.

 @param params [Hash] The request parameters from Digistore24.
 @return [Notification]
 Calculate SHA512 signature for payload.

 @return [String] The signature.