Kubernetes源码学习-APIServer-P4-APIServer的鉴权机制-蒲公英云

前言

在上一篇APIServer-P3-APIServer的认证机制中，讲述了请求进入后的认证过程，在通过认证之后，请求将进入鉴权环节，本篇就此展开。

审查请求属性

Kubernetes 仅审查以下 API 请求属性：

用户 - 身份验证期间提供的 user 字符串。
组 - 经过身份验证的用户所属的组名列表。
额外信息 - 由身份验证层提供的任意字符串键到字符串值的映射。
API - 指示请求是否针对 API 资源。
请求路径 - 各种非资源端点的路径，如 /api 或 /healthz。
API 请求动词 - API 动词 get、list、create、update、patch、watch、 proxy、redirect、delete 和 deletecollection 用于资源请求。要确定资源 API 端点的请求动词，请参阅确定请求动词。
HTTP 请求动词 - HTTP 动词 get、post、put 和 delete 用于非资源请求。
Resource - 正在访问的资源的 ID 或名称（仅限资源请求）- 对于使用 get、update、patch 和 delete 动词的资源请求，你必须提供资源名称。
子资源 - 正在访问的子资源（仅限资源请求）。
名字空间 - 正在访问的对象的名称空间（仅适用于名字空间资源请求）。
API 组 - 正在访问的 API 组（仅限资源请求）。空字符串表示核心 API 组

鉴权的描述

鉴权策略分类

目前支持6种鉴权策略，每种鉴权策略对应一个鉴权器，使用的鉴权策略需要在APIServer启动时以参数--authorization-mode的形式指定，多种策略同时指定时使用’,’号连接：

策略分类有：

--authorization-mode=ABAC 基于属性的访问控制（ABAC）模式允许你使用本地文件配置策略。
--authorization-mode=RBAC 基于角色的访问控制（RBAC）模式允许你使用 Kubernetes API 创建和存储策略。
--authorization-mode=Webhook WebHook 是一种 HTTP 回调模式，允许你使用远程 REST 端点管理鉴权。
--authorization-mode=Node 节点鉴权是一种特殊用途的鉴权模式，专门对 kubelet 发出的 API 请求执行鉴权。
--authorization-mode=AlwaysDeny 该标志阻止所有请求。仅将此标志用于测试。
--authorization-mode=AlwaysAllow 此标志允许所有请求。仅在你不需要 API 请求的鉴权时才使用此标志。

与上一篇的认证模块不同的是，当配置多个鉴权模块时，鉴权模块按顺序检查，靠前的模块具有更高的优先级来允许或拒绝请求。

来看看现有的kubeadm部署集群启用的鉴权策略:

可以看到，默认启用了Node授权和RBAC授权模块。

鉴权结果

对于每一个请求的鉴权结果，有专门为其设计的健全结果描述结构体，如下:

vendor/k8s.io/apiserver/pkg/authorization/authorizer/interfaces.go:148

type Decision int
const (
    // 拒绝
    DecisionDeny Decision = iota
    // 允许，则鉴权流程视为成功，请求顺利进入
    DecisionAllow
    // 无操作，进入下一个鉴权模块，相当于pass
    DecisionNoOpinion
)

鉴权接口方法

vendor/k8s.io/apiserver/pkg/authorization/authorizer/interfaces.go:69

// Authorizer makes an authorization decision based on information gained by making
// zero or more calls to methods of the Attributes interface. It returns nil when an action is
// authorized, otherwise it returns an error.
type Authorizer interface { 
    Authorize(a Attributes) (authorized Decision, reason string, err error)
}

所有的鉴权模块(鉴权器)都要实现这个Authorize方法,返回鉴权结果。

规则解析器

规则解析器可以根据认证之后所得到的用户信息，获取该用户对应的资源对象的操作权限。

// RuleResolver provides a mechanism for resolving the list of rules that apply to a given user within a namespace.
type RuleResolver interface { 
    // RulesFor get the list of cluster wide rules, the list of rules in the specific namespace, incomplete status and errors.
    RulesFor(user user.Info, namespace string) ([]ResourceRuleInfo, []NonResourceRuleInfo, bool, error)
}

以这里的返回值类型ResourceRuleInfo为例，默认的DefaultResourceRuleInfo结构体是这样的:

vendor/k8s.io/apiserver/pkg/authorization/authorizer/rule.go:31

// DefaultResourceRuleInfo holds information that describes a rule for the resource
type DefaultResourceRuleInfo struct { 
    Verbs         []string
    APIGroups     []string
    Resources     []string
    ResourceNames []string
}

例如对pod资源的任意操作权限的描述可以描述为:

DefaultResourceRuleInfo{ 
    Verbs         []string{ "*"}
    APIGroups     []string{ "*"}
    Resources     []string{ "pod"}
}

这个DefaultResourceRuleInfo对象描述的规则是，允许对所有api group 的pod资源进行的所有类型的操作，包括{“get”, “list”, “update”, “patch”,“create”, “delete”, “watch”, “deletecollection”}操作。

鉴权流程图

鉴权器

AlwaysAllow和AlwaysDeny这两种鉴权器很少使用，就不看了，直接略过.

ABAC鉴权器

简介

基于属性的访问控制（Attribute-based access control - ABAC）定义了访问控制范例，其中通过使用将属性组合在一起的策略来向用户授予访问权限。

启用ABAC鉴权器需要额外增加一个--authorization-policy-file=SOME_FILENAME参数，指定一个json格式的文件预设鉴权策略，是一种静态的权限配置方式。json格式样例如下：

// 授予pod资源的任意操作权限给用户podManager
{ 
    "apiVersion":"abac.authorization.kubernetes.io/v1beta1",
    "kind":"Policy",
    "spec":{ 
        "user":"podManager",
        "namespace":"*",
        "resource":"pods",
        "readonly":true
    }
}

代码实现

pkg/auth/authorizer/abac/abac.go:224

// Authorizer implements authorizer.Authorize
func (pl policyList) Authorize(a authorizer.Attributes) (authorizer.Decision, string, error) { 
    for _, p := range pl { 
        if matches(*p, a) { 
            return authorizer.DecisionAllow, "", nil
        }
    }
    return authorizer.DecisionNoOpinion, "No policy matched.", nil
}

–> pkg/auth/authorizer/abac/abac.go:117

func matches(p abac.Policy, a authorizer.Attributes) bool { 
    if subjectMatches(p, a.GetUser()) { 
    // 操作类型与规则匹配
        if verbMatches(p, a) { 
            // Resource and non-resource requests are mutually exclusive, at most one will match a policy
      // 资源类型与规则匹配(包含namespace/APIGroup/Resource)
            if resourceMatches(p, a) { 
                return true
            }
      // 针对非资源对象的操作匹配(请求路径匹配)
            if nonResourceMatches(p, a) { 
                return true
            }
        }
    }
    return false
}

RBAC鉴权器

简介

基于角色（Role）的访问控制（RBAC）是一种基于组织中用户的角色来调节控制对计算机或网络资源的访问的方法。

RBAC 鉴权机制使用 rbac.authorization.k8s.io API 组来驱动鉴权决定，允许你通过 Kubernetes API 动态配置策略。

通过创建Role 或ClusterRole来描述具体的资源授权策略，再通过创建RoleBinding/ClusterRoleBinding将策略绑定到用户/群组/服务上。

RBAC模式的详细描述和使用样例请参考我之前的文章：

k8s(十四)、RBAC权限控制

代码实现

plugin/pkg/auth/authorizer/rbac/rbac.go:74

func (r *RBACAuthorizer) Authorize(requestAttributes authorizer.Attributes) (authorizer.Decision, string, error) { 
    ruleCheckingVisitor := &authorizingVisitor{ requestAttributes: requestAttributes}
  // 规则解析器解析请求的属性，返回鉴权结果，判断匹配用的是ruleCheckingVisitor.visit方法
    r.authorizationRuleResolver.VisitRulesFor(requestAttributes.GetUser(), requestAttributes.GetNamespace(), ruleCheckingVisitor.visit)
    if ruleCheckingVisitor.allowed { 
        return authorizer.DecisionAllow, ruleCheckingVisitor.reason, nil
    }
    ...
    reason := ""
    if len(ruleCheckingVisitor.errors) > 0 { 
        reason = fmt.Sprintf("RBAC: %v", utilerrors.NewAggregate(ruleCheckingVisitor.errors))
    }
    return authorizer.DecisionNoOpinion, reason, nil
}

对比规则和请求属性，返回true or false的visit方法：

plugin/pkg/auth/authorizer/rbac/rbac.go:62

func (v *authorizingVisitor) visit(source fmt.Stringer, rule *rbacv1.PolicyRule, err error) bool { 
    if rule != nil && RuleAllows(v.requestAttributes, rule) { 
    // 请求与规则匹配，则鉴权成功
        v.allowed = true
        v.reason = fmt.Sprintf("RBAC: allowed by %s", source.String())
    // 返回false是为了提前break鉴权过程
        return false
    }
    if err != nil { 
        v.errors = append(v.errors, err)
    }
    return true
}

获取规则并调用visit方法的是VisitRulesFor接口方法，找一下VisitRulesFor方法:

pkg/registry/rbac/validation/rule.go:178

func (r *DefaultRuleResolver) VisitRulesFor(user user.Info, namespace string, visitor func(source fmt.Stringer, rule *rbacv1.PolicyRule, err error) bool) { 
  // 先拿到所有的ClusterRoleBinding对象，ClusterRoleBinding资源是cluster级别的，不区分命名空间
    if clusterRoleBindings, err := r.clusterRoleBindingLister.ListClusterRoleBindings(); err != nil { 
        if !visitor(nil, nil, err) { 
            return
        }
    } else { 
        sourceDescriber := &clusterRoleBindingDescriber{ }
        for _, clusterRoleBinding := range clusterRoleBindings { 
      // clusterRoleBinding.Subjects指定的绑定的用户对象，对比请求的所属用户，不匹配则continue
            subjectIndex, applies := appliesTo(user, clusterRoleBinding.Subjects, "")
            if !applies { 
                continue
            }
            rules, err := r.GetRoleReferenceRules(clusterRoleBinding.RoleRef, "")
            if err != nil { 
                if !visitor(nil, nil, err) { 
                    return
                }
                continue
            }
            sourceDescriber.binding = clusterRoleBinding
            sourceDescriber.subject = &clusterRoleBinding.Subjects[subjectIndex]
            for i := range rules { 
        // visit方法返回false是代表鉴权成功了，提前break鉴权过程
                if !visitor(sourceDescriber, &rules[i], nil) { 
                    return
                }
            }
        }
    }
  // 如果指定了namespace，再取命名空间级别的roleBinding资源对象，重复一次上面的过程
    if len(namespace) > 0 { 
        if roleBindings, err := r.roleBindingLister.ListRoleBindings(namespace); err != nil { 
            if !visitor(nil, nil, err) { 
                return
            }
        } else { 
            sourceDescriber := &roleBindingDescriber{ }
            for _, roleBinding := range roleBindings { 
                subjectIndex, applies := appliesTo(user, roleBinding.Subjects, namespace)
                if !applies { 
                    continue
                }
                rules, err := r.GetRoleReferenceRules(roleBinding.RoleRef, namespace)
                if err != nil { 
                    if !visitor(nil, nil, err) { 
                        return
                    }
                    continue
                }
                sourceDescriber.binding = roleBinding
                sourceDescriber.subject = &roleBinding.Subjects[subjectIndex]
                for i := range rules { 
                    if !visitor(sourceDescriber, &rules[i], nil) { 
                        return
                    }
                }
            }
        }
    }
}

过程总结

参考代码片中的注释，rbac鉴权过程如下:

1.取到所有的clusterRoleBinding/roleBindings资源对象，遍历它们对比请求用户
2.对比roleBindings/clusterRoleBinding指向的用户(主体)与请求用户，相同则选中，不相同continue
3.对比规则与请求属性，符合则提前结束鉴权

Node鉴权器

上面有提过，node鉴权器是专为kubelet组件设计的，按照kubeadm集群的默认配置，它是排序在第一位的鉴权器，为什么把它放在后面再讲呢，因为node鉴权器本质上也是利用了rbac鉴权器，是通过为system:node这个内置用户授权来实现的，来看一下。

默认Node规则生成

plugin/pkg/auth/authorizer/rbac/bootstrappolicy/policy.go:97

func NodeRules() []rbacv1.PolicyRule { 
    nodePolicyRules := []rbacv1.PolicyRule{ 
        // Needed to check API access. These creates are non-mutating
        rbacv1helpers.NewRule("create").Groups(authenticationGroup).Resources("tokenreviews").RuleOrDie(),
        rbacv1helpers.NewRule("create").Groups(authorizationGroup).Resources("subjectaccessreviews", "localsubjectaccessreviews").RuleOrDie(),
        // Needed to build serviceLister, to populate env vars for services
        rbacv1helpers.NewRule(Read...).Groups(legacyGroup).Resources("services").RuleOrDie(),
        // Nodes can register Node API objects and report status.
        // Use the NodeRestriction admission plugin to limit a node to creating/updating its own API object.
        rbacv1helpers.NewRule("create", "get", "list", "watch").Groups(legacyGroup).Resources("nodes").RuleOrDie(),
        rbacv1helpers.NewRule("update", "patch").Groups(legacyGroup).Resources("nodes/status").RuleOrDie(),
        rbacv1helpers.NewRule("update", "patch").Groups(legacyGroup).Resources("nodes").RuleOrDie(),
        // TODO: restrict to the bound node as creator in the NodeRestrictions admission plugin
        rbacv1helpers.NewRule("create", "update", "patch").Groups(legacyGroup).Resources("events").RuleOrDie(),
        // TODO: restrict to pods scheduled on the bound node once field selectors are supported by list/watch authorization
        rbacv1helpers.NewRule(Read...).Groups(legacyGroup).Resources("pods").RuleOrDie(),
        // Needed for the node to create/delete mirror pods.
        // Use the NodeRestriction admission plugin to limit a node to creating/deleting mirror pods bound to itself.
        rbacv1helpers.NewRule("create", "delete").Groups(legacyGroup).Resources("pods").RuleOrDie(),
        // Needed for the node to report status of pods it is running.
        // Use the NodeRestriction admission plugin to limit a node to updating status of pods bound to itself.
        rbacv1helpers.NewRule("update", "patch").Groups(legacyGroup).Resources("pods/status").RuleOrDie(),
        // Needed for the node to create pod evictions.
        // Use the NodeRestriction admission plugin to limit a node to creating evictions for pods bound to itself.
        rbacv1helpers.NewRule("create").Groups(legacyGroup).Resources("pods/eviction").RuleOrDie(),
        // Needed for imagepullsecrets, rbd/ceph and secret volumes, and secrets in envs
        // Needed for configmap volume and envs
        // Use the Node authorization mode to limit a node to get secrets/configmaps referenced by pods bound to itself.
        rbacv1helpers.NewRule("get", "list", "watch").Groups(legacyGroup).Resources("secrets", "configmaps").RuleOrDie(),
        // Needed for persistent volumes
        // Use the Node authorization mode to limit a node to get pv/pvc objects referenced by pods bound to itself.
        rbacv1helpers.NewRule("get").Groups(legacyGroup).Resources("persistentvolumeclaims", "persistentvolumes").RuleOrDie(),
        // TODO: add to the Node authorizer and restrict to endpoints referenced by pods or PVs bound to the node
        // Needed for glusterfs volumes
        rbacv1helpers.NewRule("get").Groups(legacyGroup).Resources("endpoints").RuleOrDie(),
        // Used to create a certificatesigningrequest for a node-specific client certificate, and watch
        // for it to be signed. This allows the kubelet to rotate it's own certificate.
        rbacv1helpers.NewRule("create", "get", "list", "watch").Groups(certificatesGroup).Resources("certificatesigningrequests").RuleOrDie(),
    }
    if utilfeature.DefaultFeatureGate.Enabled(features.ExpandPersistentVolumes) { 
        // Use the Node authorization mode to limit a node to update status of pvc objects referenced by pods bound to itself.
        // Use the NodeRestriction admission plugin to limit a node to just update the status stanza.
        pvcStatusPolicyRule := rbacv1helpers.NewRule("get", "update", "patch").Groups(legacyGroup).Resources("persistentvolumeclaims/status").RuleOrDie()
        nodePolicyRules = append(nodePolicyRules, pvcStatusPolicyRule)
    }
    if utilfeature.DefaultFeatureGate.Enabled(features.TokenRequest) { 
        // Use the Node authorization to limit a node to create tokens for service accounts running on that node
        // Use the NodeRestriction admission plugin to limit a node to create tokens bound to pods on that node
        tokenRequestRule := rbacv1helpers.NewRule("create").Groups(legacyGroup).Resources("serviceaccounts/token").RuleOrDie()
        nodePolicyRules = append(nodePolicyRules, tokenRequestRule)
    }
    // CSI
    if utilfeature.DefaultFeatureGate.Enabled(features.CSIPersistentVolume) { 
        volAttachRule := rbacv1helpers.NewRule("get").Groups(storageGroup).Resources("volumeattachments").RuleOrDie()
        nodePolicyRules = append(nodePolicyRules, volAttachRule)
        if utilfeature.DefaultFeatureGate.Enabled(features.CSIDriverRegistry) { 
            csiDriverRule := rbacv1helpers.NewRule("get", "watch", "list").Groups("storage.k8s.io").Resources("csidrivers").RuleOrDie()
            nodePolicyRules = append(nodePolicyRules, csiDriverRule)
        }
    }
    if utilfeature.DefaultFeatureGate.Enabled(features.KubeletPluginsWatcher) &&
        utilfeature.DefaultFeatureGate.Enabled(features.CSINodeInfo) { 
        csiNodeInfoRule := rbacv1helpers.NewRule("get", "create", "update", "patch", "delete").Groups("storage.k8s.io").Resources("csinodes").RuleOrDie()
        nodePolicyRules = append(nodePolicyRules, csiNodeInfoRule)
    }
    // Node leases
    if utilfeature.DefaultFeatureGate.Enabled(features.NodeLease) { 
        nodePolicyRules = append(nodePolicyRules, rbacv1helpers.NewRule("get", "create", "update", "patch", "delete").Groups("coordination.k8s.io").Resources("leases").RuleOrDie())
    }
    // RuntimeClass
    if utilfeature.DefaultFeatureGate.Enabled(features.RuntimeClass) { 
        nodePolicyRules = append(nodePolicyRules, rbacv1helpers.NewRule("get", "list", "watch").Groups("node.k8s.io").Resources("runtimeclasses").RuleOrDie())
    }
    return nodePolicyRules
}

这里初始化了kubelet工作所需要的资源的权限，如(node/pod/cm/secret/pvc等)

Authorize代码实现

plugin/pkg/auth/authorizer/node/node_authorizer.go:80

func (r *NodeAuthorizer) Authorize(attrs authorizer.Attributes) (authorizer.Decision, string, error) { 
  // 判断是不是node发起的请求(所属的group是不是system:node)
    nodeName, isNode := r.identifier.NodeIdentity(attrs.GetUser())
    if !isNode { 
        // reject requests from non-nodes
        return authorizer.DecisionNoOpinion, "", nil
    }
    if len(nodeName) == 0 { 
        // reject requests from unidentifiable nodes
        klog.V(2).Infof("NODE DENY: unknown node for user %q", attrs.GetUser().GetName())
        return authorizer.DecisionNoOpinion, fmt.Sprintf("unknown node for user %q", attrs.GetUser().GetName()), nil
    }
    // subdivide access to specific resources
    if attrs.IsResourceRequest() { 
    // 根据请求属性(路径)获取资源类型，不同类型资源不同的方式处理
        requestResource := schema.GroupResource{ Group: attrs.GetAPIGroup(), Resource: attrs.GetResource()}
        switch requestResource { 
        case secretResource:
            return r.authorizeReadNamespacedObject(nodeName, secretVertexType, attrs)
        case configMapResource:
            return r.authorizeReadNamespacedObject(nodeName, configMapVertexType, attrs)
        case pvcResource:
            if r.features.Enabled(features.ExpandPersistentVolumes) { 
                if attrs.GetSubresource() == "status" { 
                    return r.authorizeStatusUpdate(nodeName, pvcVertexType, attrs)
                }
            }
            return r.authorizeGet(nodeName, pvcVertexType, attrs)
        case pvResource:
            return r.authorizeGet(nodeName, pvVertexType, attrs)
        case vaResource:
            if r.features.Enabled(features.CSIPersistentVolume) { 
                return r.authorizeGet(nodeName, vaVertexType, attrs)
            }
            return authorizer.DecisionNoOpinion, fmt.Sprintf("disabled by feature gate %s", features.CSIPersistentVolume), nil
        case svcAcctResource:
            if r.features.Enabled(features.TokenRequest) { 
                return r.authorizeCreateToken(nodeName, serviceAccountVertexType, attrs)
            }
            return authorizer.DecisionNoOpinion, fmt.Sprintf("disabled by feature gate %s", features.TokenRequest), nil
        case leaseResource:
            if r.features.Enabled(features.NodeLease) { 
                return r.authorizeLease(nodeName, attrs)
            }
            return authorizer.DecisionNoOpinion, fmt.Sprintf("disabled by feature gate %s", features.NodeLease), nil
        case csiNodeResource:
            if r.features.Enabled(features.KubeletPluginsWatcher) && r.features.Enabled(features.CSINodeInfo) { 
                return r.authorizeCSINode(nodeName, attrs)
            }
            return authorizer.DecisionNoOpinion, fmt.Sprintf("disabled by feature gates %s and %s", features.KubeletPluginsWatcher, features.CSINodeInfo), nil
        }
    }
    // Access to other resources is not subdivided, so just evaluate against the statically defined node rules
    if rbac.RulesAllow(attrs, r.nodeRules...) { 
        return authorizer.DecisionAllow, "", nil
    }
    return authorizer.DecisionNoOpinion, "", nil
}

WebHook鉴权器

简介

与上一篇中的WebHook认证器类似，WebHook鉴权器也是依赖于集群外部的鉴权服务器，将鉴权请求POST发送给外部的鉴权服务器。

Webhook 模式需要一个 HTTP 配置文件，通过 --authorization-webhook-config-file=SOME_FILENAME 的参数声明。

配置文件的格式使用 kubeconfig。在文件中，“users” 代表着 API 服务器的 webhook，而 “cluster” 代表着远程服务。

使用 HTTPS 客户端认证的配置例子：

# Kubernetes API 版本
apiVersion: v1
# API 对象种类
kind: Config
# clusters 代表远程服务。
clusters:
  - name: name-of-remote-authz-service
    cluster:
      # 对远程服务进行身份认证的 CA。
      certificate-authority: /path/to/ca.pem
      # 远程服务的查询 URL。必须使用 'https'。
      server: https://authz.example.com/authorize
# users 代表 API 服务器的 webhook 配置
users:
  - name: name-of-api-server
    user:
      client-certificate: /path/to/cert.pem # webhook plugin 使用 cert
      client-key: /path/to/key.pem          # cert 所对应的 key
# kubeconfig 文件必须有 context。需要提供一个给 API 服务器。
current-context: webhook
contexts:
- context:
    cluster: name-of-remote-authz-service
    user: name-of-api-server
  name: webhook

摘自官方文档Webhook 模式

代码实现

vendor/k8s.io/apiserver/plugin/pkg/authorizer/webhook/webhook.go:152

func (w *WebhookAuthorizer) Authorize(attr authorizer.Attributes) (decision authorizer.Decision, reason string, err error) { 
    r := &authorization.SubjectAccessReview{ }
    if user := attr.GetUser(); user != nil { 
        r.Spec = authorization.SubjectAccessReviewSpec{ 
            User:   user.GetName(),
            UID:    user.GetUID(),
            Groups: user.GetGroups(),
            Extra:  convertToSARExtra(user.GetExtra()),
        }
    }
    if attr.IsResourceRequest() { 
        r.Spec.ResourceAttributes = &authorization.ResourceAttributes{ 
            Namespace:   attr.GetNamespace(),
            Verb:        attr.GetVerb(),
            Group:       attr.GetAPIGroup(),
            Version:     attr.GetAPIVersion(),
            Resource:    attr.GetResource(),
            Subresource: attr.GetSubresource(),
            Name:        attr.GetName(),
        }
    } else { 
        r.Spec.NonResourceAttributes = &authorization.NonResourceAttributes{ 
            Path: attr.GetPath(),
            Verb: attr.GetVerb(),
        }
    }
  // 将请求的主体/资源/操作等字段放在一个json里
    key, err := json.Marshal(r.Spec)
    if err != nil { 
        return w.decisionOnError, "", err
    }
  // 从本地的缓存里取，有则不发起远端post请求了
    if entry, ok := w.responseCache.Get(string(key)); ok { 
        r.Status = entry.(authorization.SubjectAccessReviewStatus)
    } else { 
        var (
            result *authorization.SubjectAccessReview
            err    error
        )
        webhook.WithExponentialBackoff(w.initialBackoff, func() error { 
      // 缓存里没有，则发起post请求给远端鉴权服务器
            result, err = w.subjectAccessReview.Create(r)
            return err
        })
        if err != nil { 
            // An error here indicates bad configuration or an outage. Log for debugging.
            klog.Errorf("Failed to make webhook authorizer request: %v", err)
            return w.decisionOnError, "", err
        }
        r.Status = result.Status
    // 长度不超过10000则缓存结果
        if shouldCache(attr) { 
            if r.Status.Allowed { 
                w.responseCache.Add(string(key), r.Status, w.authorizedTTL)
            } else { 
                w.responseCache.Add(string(key), r.Status, w.unauthorizedTTL)
            }
        }
    }
    switch { 
    // 根据远端鉴权服务器的响应状态，返回鉴权结果
    case r.Status.Denied && r.Status.Allowed:
        return authorizer.DecisionDeny, r.Status.Reason, fmt.Errorf("webhook subject access review returned both allow and deny response")
    case r.Status.Denied:
        return authorizer.DecisionDeny, r.Status.Reason, nil
    case r.Status.Allowed:
        return authorizer.DecisionAllow, r.Status.Reason, nil
    default:
        return authorizer.DecisionNoOpinion, r.Status.Reason, nil
    }
}