class Aws::S3::ExpressCredentials

def create_session_options
  @cso ||= begin
    input = S3::Client.api.operation(:create_session).input
    Set.new(input.shape.member_names)
  end
end

def initialize(options = {})
  @client = options[:client]
  @create_session_params = {}
  options.each_pair do |key, value|
    if self.class.create_session_options.include?(key)
      @create_session_params[key] = value
    end
  end
  @async_refresh = true
  super
end

def refresh
  c = @client.create_session(@create_session_params).credentials
  @credentials = Credentials.new(
    c.access_key_id,
    c.secret_access_key,
    c.session_token
  )
  @expiration = c.expiration
end