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)
  namespaceSelector:
    labelSelector:
      matchExpressions:
      - key: stage
        operator: In
        values:
        - test
        - review
      matchLabels:
        team: frontend

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

You may need to create a ServiceAccount with access to the Kubernetes API when, for example, an application is deployed using a CI system.

1. Create a ServiceAccount, e.g., in the d8-service-accounts namespace:

   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 it the necessary privileges (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 multitenancy is enabled in the Deckhouse configuration (the enableMultiTenancy paameter; it is only available in Enterprise Edition), configure the namespaces the ServiceAccount has access to (the namespaceSelector parameter).

3. Set the variable values (they will be used later) by running the following commands (insert your own values):

   export CLUSTER_NAME=my-cluster
   export USER_NAME=gitlab-runner-deploy.my-cluster
   export CONTEXT_NAME=${CLUSTER_NAME}-${USER_NAME}
   export FILE_NAME=kube.config
   

4. Generate the cluster section in the kubectl configuration file:

   Use one of the following options to access the cluster API server:

   • If there is direct access to the API server:

     1. Get a Kubernetes cluster CA certificate:

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

     2. Generate the cluster section (the API server’s IP address is used for access):

        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, use one of the following options:
     • enable access to the API-server over the Ingress controller (the publishAPI parameter) and specify the addresses from which requests originate (the whitelistSourceRanges parameter);
     • specify addresses from which requests will originate in a separate Ingress controller (the acceptRequestsFrom parameter).

   • If a non-public CA is used:

     1. Get the CA certificate from the Secret with the certificate that is used for the api.%s domain:

        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 the cluster section (an external domain and a CA for access are used):

        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 a public CA is used. Generate the cluster section (an external domain is used for access):

     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
     

5. Generate the user section using the token from the Secret’s ServiceAccount in the kubectl configuration file:

   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
   

6. Generate the context in the kubectl configuration file:

   kubectl config set-context $CONTEXT_NAME \
     --cluster=$CLUSTER_NAME --user=$USER_NAME \
     --kubeconfig=$FILE_NAME
   

7. Set the generated context as the default one in the kubectl configuration 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