# File lib/aws/default_signer.rb, line 40
    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