drivers/azure/azureutil/auth.go
func validateToken(env azure.Environment, token *azure.ServicePrincipalToken) error {
	c := subscriptionsClient(env.ResourceManagerEndpoint)
	c.Authorizer = token
	_, err := c.List()
	if err != nil {
		return fmt.Errorf("Token validity check failed: %v", err)
	}
	return nil
}
func validateToken(env azure.Environment, token *azure.ServicePrincipalToken) error {
	c := subscriptionsClient(env.ResourceManagerEndpoint)
	c.Authorizer = token
	_, err := c.List()
	if err != nil {
		return fmt.Errorf("Token validity check failed: %v", err)
	}
	return nil
}
// validateToken makes a call to Azure SDK with given token, essentially making
// sure if the access_token valid, if not it uses SDK’s functionality to
// automatically refresh the token using refresh_token (which might have
// expired). This check is essentially to make sure refresh_token is good.