module AWS::Core::Signature::Version2

def add_authorization! credentials
  add_param('AWSAccessKeyId', credentials.access_key_id)
  if token = credentials.session_token
    add_param("SecurityToken", token)
  end
  add_param('SignatureVersion', '2')
  add_param('SignatureMethod', 'HmacSHA256')
  add_param('Signature', signature(credentials))
  self.body = url_encoded_params
end