Kubernetes源码学习-APIServer-P4-APIServer的鉴权机制

た入场券 2022-10-27 12:29 242阅读 0赞

## 前言 ##

在上一篇[**APIServer-P3-APIServer的认证机制**][APIServer-P3-APIServer]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][Link 1]。
 *  **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][API] （仅限资源请求）。空字符串表示[核心 API 组][API 1]

## 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:

![f4ca97ec0aa4f71ca80f4937d25dfbc5.png][]

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 ###

![f30cfa9babebc9700d626df79028f2e6.png][]

## 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][API] 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][k8s_RBAC]

#### 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][Webhook]

#### 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
    	}
    
    }

## 总结 ##

鉴权的流程与认证的流程大体类似，但也有所不同，例如认证器链的执行顺序是无序的，而鉴权器链的执行顺序是有序的(按参数指定的顺序)。另外鉴权器的数量没有认证器那么多，因此相对容易理解一些。

[APIServer-P3-APIServer]: https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/apiServer/Kubernetes%E6%BA%90%E7%A0%81%E5%AD%A6%E4%B9%A0-APIServer-P3-APIServer%E7%9A%84%E8%AE%A4%E8%AF%81%E6%9C%BA%E5%88%B6.md
[Link 1]: https://kubernetes.io/zh/docs/reference/access-authn-authz/authorization/#determine-the-request-verb
[API]: https://kubernetes.io/zh/docs/concepts/overview/kubernetes-api/#api-groups
[API 1]: https://kubernetes.io/zh/docs/reference/using-api/#api-groups
[f4ca97ec0aa4f71ca80f4937d25dfbc5.png]: /images/20221024/33550589f73c4339be37ec6bd8e8da8a.png
[f30cfa9babebc9700d626df79028f2e6.png]: /images/20221024/06e7f6dcf31e481badf1ea6546fbd98b.png
[k8s_RBAC]: https://blog.upweto.top/2018/12/06/k8s%28%E5%8D%81%E5%9B%9B%29%E3%80%81RBAC%E6%9D%83%E9%99%90%E6%8E%A7%E5%88%B6.html
[kubeconfig]: https://kubernetes.io/zh/docs/tasks/access-application-cluster/configure-access-multiple-clusters/
[Webhook]: https://kubernetes.io/zh/docs/reference/access-authn-authz/webhook/