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User Management

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rgaudin edited this page Mar 21, 2022 · 5 revisions

Master authentication (⚠️ don't use it)

Scaleway provides a token-based authentication for username kubernetes-admin which is hardcoded into system:masters group (maybe using --token-auth-file on apiserver).

It's possible to reset the admin token using scaleway UI/API.

Our use case

  • nobody should use the master token.
  • authentication is done using certificates (see how to create below)
  • no Role or ClusterRole binding to groups
  • groups are solely uses as labels

Creating a User

Note: once a certificate is issued to a User, it cannot be revoked so the issuer will be able to authenticate to the Cluster for as long as the certificate has not expired. Set expiration accordingly. It's easy to recreate a certificate so don't go beyond a year (31536000s).

Create Certificate

Note: you'll need the cluster's CA certificate to prepare the kubeconfig. This is done once

# download the cluster's CA cert
kubectl get configmap kube-root-ca.crt -o json |jq -r '.data."ca.crt"' > ca.crt
# fill-out
CLUSTERURL=https://some-id.api.k8s.fr-par.scw.cloud:6443
USERNAME=some-username
GROUPNAME=group-a
CERTIFICATE_NAME=user-$USERNAME

openssl genrsa -out ${USERNAME}.key 2048

CSR_FILE=$USERNAME.csr
KEY_FILE=$USERNAME.key
CRT_FILE=$USERNAME.crt

openssl req -new -key $KEY_FILE -out $CSR_FILE -subj "/CN=$USERNAME/O=$GROUPNAME"

cat <<EOF | kubectl create -f -
apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: $CERTIFICATE_NAME 
spec:
  groups:
  - system:authenticated
  request: $(cat $CSR_FILE | base64 | tr -d '\n')
  signerName: kubernetes.io/kube-apiserver-client6
  # one year expiration
  expirationSeconds: 31536000
  usages:
  - client auth
EOF

kubectl certificate approve $CERTIFICATE_NAME

kubectl get csr $CERTIFICATE_NAME -o jsonpath='{.status.certificate}' | base64 -d > $CRT_FILE

Export a kubeconfig file

CONFIGNAME=kiwix-$USERNAME.config
kubectl config --kubeconfig $CONFIGNAME set-credentials $USERNAME --client-key=$KEY_FILE --client-certificate=$CRT_FILE --embed-certs=true

kubectl config --kubeconfig $CONFIGNAME set-cluster kiwix --embed-certs --certificate-authority=ca.crt --server=$CLUSTERURL
kubectl config --kubeconfig $CONFIGNAME set-context $USERNAME@kiwix --cluster=kiwix --user=$USERNAME --namespace=$NAMESPACE
kubectl config --kubeconfig $CONFIGNAME use-context $USERNAME@kiwix

Now securely it transmit it to the user. ⚠️ it's a plain text (yaml) file with credentials.

User will now be able to authenticate with the Cluster but has no authorization.

Authorize User

Manually bind User to Roles on namespaces and ClusterRole on namespaces or Cluster-wide.

  • Use per-user bindings with user- prefixed names to ease removal (very important)
  • Use user-listed shared bindings for known, stable groups (coreteam)
  • Provide least required number of permissions and roles

Sample binding: use appropriate ones for User

cat <<EOF | kubectl create -f -
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: user-$USERNAME-view-binding
subjects:
- name: $USERNAME
  kind: User
  namespace: $NAMESPACE
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: view
EOF

Using credentials

Once exported as a kubeconfig file, can be used directly with kubectl

export KUBECONFIG=./username.config
kubectl --kubeconfig ./username.config

Editing a User's access

Editing a User's access is done by adding or removing bindings. Should a Role or ClusterRole satisfying the requirements not be present, this should be created first then a binding added.

Special group of known, limited users would uses combined bindings which would contain multiple User subjects. Should a user need to be added or removed from one of those group, the bindings for the group would be updated to include/remove the User's subject.

Removing a user

Kubernetes has no notion of User so it's not possible to delete one. What should be done instead is to remove all authorizations associated with the User (its username string).

There is currently no way to revoke a certificate in k8s so the User will still be able to authenticate (until certificate expiration)

for binding in $(kubectl get clusterrolebindings -o name |grep user-$USERNAME-); do kubectl delete $binding; done
for binding in $(kubectl get rolebindings -o name |grep user-$USERNAME-); do kubectl delete $binding; done

References

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