The user-authz module: usage

An example of ClusterAuthorizationRule

apiVersion: deckhouse.io/v1
kind: ClusterAuthorizationRule
metadata:
  name: test-rule
spec:
  subjects:
  - kind: User
    name: some@example.com
  - kind: ServiceAccount
    name: gitlab-runner-deploy
    namespace: d8-service-accounts
  - kind: Group
    name: some-group-name
  accessLevel: PrivilegedUser
  portForwarding: true
  # This option is only available if the enableMultiTenancy parameter is set (Enterprise Edition version)
  allowAccessToSystemNamespaces: false
  # This option is only available if the enableMultiTenancy parameter is set (Enterprise Edition version)
  limitNamespaces:
  - review-.*
  - stage

Creating a user

There are two types of users in Kubernetes:

• Service accounts managed by Kubernetes via the API;
• Regular users managed by some external tool that the cluster administrator configures. There are many authentication mechanisms and, accordingly, many ways to create users. Currently, two authentication methods are supported:
  • Via the user-authn module.
  • Via the certificates.

When issuing the authentication certificate, you need to specify the name (CN=<name>), the required number of groups (O=<group>), and sign it using the root CA of the cluster. It is this mechanism that authenticates you in the cluster when, for example, you use kubectl on a bastion node.

Creating a ServiceAccount for a machine and granting it access

It may be required to give your machine static access to the Kubernetes API, e.g., for deploying applications from a CI system runner.

1. Create a ServiceAccount in the d8-service-accounts namespace (you can change the name):

   kubectl create -f - <<EOF
   apiVersion: v1
   kind: ServiceAccount
   metadata:
     name: gitlab-runner-deploy
     namespace: d8-service-accounts
   ---
   apiVersion: v1
   kind: Secret
   metadata:
     name: gitlab-runner-deploy-token
     namespace: d8-service-accounts
     annotations:
       kubernetes.io/service-account.name: gitlab-runner-deploy
   type: kubernetes.io/service-account-token
   EOF
   

2. Grant the necessary rights to the ServiceAccount (using the ClusterAuthorizationRule custom resource):

   kubectl create -f - <<EOF
   apiVersion: deckhouse.io/v1
   kind: ClusterAuthorizationRule
   metadata:
     name: gitlab-runner-deploy
   spec:
     subjects:
     - kind: ServiceAccount
       name: gitlab-runner-deploy
       namespace: d8-service-accounts
     accessLevel: SuperAdmin
     # This option is only available if the enableMultiTenancy parameter is set (Enterprise Edition version)
     allowAccessToSystemNamespaces: true
   EOF
   

   If the multitenancy mode is enabled in the Deckhouse configuration, you need to specify the allowAccessToSystemNamespaces: true parameter to give the ServiceAccount access to the system namespaces.

3. Generate a kube-config (don’t forget to substitute your values):

   cluster_name=my-cluster
   user_name=gitlab-runner-deploy.my-cluster
   context_name=${cluster_name}-${user_name}
   file_name=kube.config
   

   • The cluster section:
     • If there is direct access to the API server, then use its IP address:

       1. Get the CA of our Kubernetes cluster:

          kubectl get cm kube-root-ca.crt -o jsonpath='{ .data.ca\.crt }' > /tmp/ca.crt
          

       2. Generate a section using the API server’s IP:

          kubectl config set-cluster $cluster_name --embed-certs=true \
            --server=https://$(kubectl get ep kubernetes -o json | jq -rc '.subsets[0] | "\(.addresses[0].ip):\(.ports[0].port)"') \
            --certificate-authority=/tmp/ca.crt \
            --kubeconfig=$file_name
          

     • If there is no direct access to the API server, enable the publishAPI parameter containing the whitelistSourceRanges array. Or you can do that via a separate Ingress-controller using the ingressClass option with the finite SourceRange. That is, specify the requests’ source addresses in the acceptRequestsFrom controller parameter.

     • If the CA is non-public:

       1. Get the CA from the secret containing the api.%s domain’s certificate:

          kubectl -n d8-user-authn get secrets -o json \
            $(kubectl -n d8-user-authn get ing kubernetes-api -o jsonpath="{.spec.tls[0].secretName}") \
            | jq -rc '.data."ca.crt" // .data."tls.crt"' \
            | base64 -d > /tmp/ca.crt
          

       2. Generate a section with the external domain and CA:

          kubectl config set-cluster $cluster_name --embed-certs=true \
            --server=https://$(kubectl -n d8-user-authn get ing kubernetes-api -ojson | jq '.spec.rules[].host' -r) \
            --certificate-authority=/tmp/ca.crt \
            --kubeconfig=$file_name
          

     • If the CA is public, generate a section with just the external domain:

       kubectl config set-cluster $cluster_name \
         --server=https://$(kubectl -n d8-user-authn get ing kubernetes-api -ojson | jq '.spec.rules[].host' -r) \
         --kubeconfig=$file_name
       

   • Generate the user section using the token from the ServiceAccount secret:

     kubectl config set-credentials $user_name \
       --token=$(kubectl -n d8-service-accounts get secret gitlab-runner-deploy-token -o json |jq -r '.data["token"]' | base64 -d) \
       --kubeconfig=$file_name
     

   • Generate the context to bind it all together:

     kubectl config set-context $context_name \
       --cluster=$cluster_name --user=$user_name \
       --kubeconfig=$file_name
     

   • Set default context of your newly created kubeconfig file:

     kubectl config use-context $context_name --kubeconfig=$file_name
     

How to create a user using a client certificate

Creating a user

• Get the cluster’s root certificate (ca.crt and ca.key).

• Generate the user key:

  openssl genrsa -out myuser.key 2048
  

• Create a CSR file and specify in it the username (myuser) and groups to which this user belongs (mygroup1 & mygroup2):

  openssl req -new -key myuser.key -out myuser.csr -subj "/CN=myuser/O=mygroup1/O=mygroup2"
  

• Sign the CSR using the cluster root certificate:

  openssl x509 -req -in myuser.csr -CA ca.crt -CAkey ca.key -CAcreateserial -out myuser.crt -days 10
  

• Now you can use the certificate issued in the config file:

  cat << EOF
  apiVersion: v1
  clusters:
  - cluster:
      certificate-authority-data: $(cat ca.crt | base64 -w0)
      server: https://<cluster_host>:6443
    name: kubernetes
  contexts:
  - context:
      cluster: kubernetes
      user: myuser
    name: myuser@kubernetes
  current-context: myuser@kubernetes
  kind: Config
  preferences: {}
  users:
  - name: myuser
    user:
      client-certificate-data: $(cat myuser.crt | base64 -w0)
      client-key-data: $(cat myuser.key | base64 -w0)
  EOF
  

Granting access to the created user

To grant access to the created user, create a `ClusterAuthorizationRule’.

Example of a ClusterAuthorizationRule:

apiVersion: deckhouse.io/v1
kind: ClusterAuthorizationRule
metadata:
  name: myuser
spec:
  subjects:
  - kind: User
    name: myuser
  accessLevel: PrivilegedUser
  portForwarding: true

Configuring kube-apiserver for multi-tenancy mode

The multi-tenancy mode, which allows you to restrict access to namespaces, is enabled by the enableMultiTenancy module’s parameter.

Working in multi-tenancy mode requires enabling the Webhook authorization plugin and configuring a kube-apiserver. All actions necessary for the multi-tenancy mode are performed automatically by the control-plane-manager module; no additional steps are required.

Changes to the kube-apiserver manifest that will occur after enabling multi-tenancy mode:

• The --authorization-mode argument will be modified: the Webhook method will be added in front of the RBAC method (e.g., --authorization-mode=Node,Webhook,RBAC);
• The --authorization-webhook-config-file=/etc/kubernetes/authorization-webhook-config.yaml will be added;

• The volumeMounts parameter will be added:

  - name: authorization-webhook-config
    mountPath: /etc/kubernetes/authorization-webhook-config.yaml
    readOnly: true
  

• The volumes parameter will be added:

  - name: authorization-webhook-config
    hostPath:
      path: /etc/kubernetes/authorization-webhook-config.yaml
      type: FileOrCreate
  

How do I check that a user has access?

Execute the command below with the following parameters:

• resourceAttributes (the same as in RBAC) - target resources;
• user - the name of the user;
• groups - user groups;

You can use Dex logs to find out groups and a username if this module is used together with the user-authn module (kubectl -n d8-user-authn logs -l app=dex); logs available only if the user is authorized).

cat  <<EOF | 2>&1 kubectl  create --raw  /apis/authorization.k8s.io/v1/subjectaccessreviews -f - | jq .status
{
  "apiVersion": "authorization.k8s.io/v1",
  "kind": "SubjectAccessReview",
  "spec": {
    "resourceAttributes": {
      "namespace": "",
      "verb": "watch",
      "version": "v1",
      "resource": "pods"
    },
    "user": "system:kube-controller-manager",
    "groups": [
      "Admins"
    ]
  }
}
EOF

You will see if access is allowed and what role is used:

{
  "allowed": true,
  "reason": "RBAC: allowed by ClusterRoleBinding \"system:kube-controller-manager\" of ClusterRole \"system:kube-controller-manager\" to User \"system:kube-controller-manager\""
}

If the multitenancy mode is enabled in your cluster, you need to perform another check to be sure that the user has access to the namespace:

cat  <<EOF | 2>&1 kubectl --kubeconfig /etc/kubernetes/deckhouse/extra-files/webhook-config.yaml create --raw / -f - | jq .status
{
  "apiVersion": "authorization.k8s.io/v1",
  "kind": "SubjectAccessReview",
  "spec": {
    "resourceAttributes": {
      "namespace": "",
      "verb": "watch",
      "version": "v1",
      "resource": "pods"
    },
    "user": "system:kube-controller-manager",
    "groups": [
      "Admins"
    ]
  }
}
EOF

{
  "allowed": false
}

The allowed: false message means that the webhook doesn’t block access. In case of webhook denying the request, you will see, e.g., the following message:

{
  "allowed": false,
  "denied": true,
  "reason": "making cluster scoped requests for namespaced resources are not allowed"
}

Customizing rights of high-level roles

If you want to grant more privileges to a specific high-level role, you only need to create a ClusterRole with the user-authz.deckhouse.io/access-level: <AccessLevel> annotation.

An example:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  annotations:
    user-authz.deckhouse.io/access-level: Editor
  name: user-editor
rules:
- apiGroups:
  - kuma.io
  resources:
  - trafficroutes
  - trafficroutes/finalizers
  verbs:
  - get
  - list
  - watch
  - create
  - update
  - patch
  - delete
- apiGroups:
  - flagger.app
  resources:
  - canaries
  - canaries/status
  - metrictemplates
  - metrictemplates/status
  - alertproviders
  - alertproviders/status
  verbs:
  - get
  - list
  - watch
  - create
  - update
  - patch
  - delete