func (r SecGroupPage) NextPageURL() (string, error) {
	var s struct {
		Links []gophercloud.Link `json:"security_groups_links"`
	}
	err := r.ExtractInto(&s)
	if err != nil {
		return "", err
	}
	return gophercloud.ExtractNextURL(s.Links)
}
NextPageURL is invoked when a paginated collection of security groups has
reached the end of a page and the pager seeks to traverse over a new one. In
order to do this, it needs to construct the next page's URL.
package groups
import (
	"github.com/gophercloud/gophercloud"
	"github.com/gophercloud/gophercloud/openstack/networking/v2/extensions/security/rules"
	"github.com/gophercloud/gophercloud/pagination"
)
type SecGroup struct {
	ID string
	Name string
	Description string
	Rules []rules.SecGroupRule `json:"security_group_rules"`
	TenantID string `json:"tenant_id"`
}
type SecGroupPage struct {
	pagination.LinkedPageBase
}