func NewInstanceAuthenticator(token string, accountID int) Authenticator {
	builder := instanceLoginRequestBuilder{token: token, accountID: accountID}
	return newCookieSigner(&builder, accountID)
}
func NewInstanceAuthenticator(token string, accountID int) Authenticator {
	builder := instanceLoginRequestBuilder{token: token, accountID: accountID}
	return newCookieSigner(&builder, accountID)
}
// NewInstanceAuthenticator returns an authenticator that uses the instance facing API token to
// create sessions. This is the token found on RightLink instances under the RS_API_TOKEN
// environment variable.
// The returned authenticator takes care of refreshing the RightScale session as needed.
// Note: Use of rsc made from RightLink10 instances can use the RL10 authenticator instead.