# File lib/aws/core/default_signer.rb, line 41
      def initialize(access_key_id, secret_access_key, session_token = nil)

        @access_key_id = access_key_id
        @secret_access_key = secret_access_key
        @session_token = session_token

        raise "Missing credentials" unless access_key_id and secret_access_key

      end