Create kubeconfig with restricted permission - azure

Question

I need to create a kubeconfig with restricted access, I want to be able to provide permission to update configmap in specific namesapce, how can I create such a kubeconfig with the following permission
for specefic namespace (myns)
update only configmap (mycm)
Is there a simple way to create it ?
The tricky part here is that I need that some program will have access to cluster X and modify only this comfigMap, How would I do it from outside process without providing the full kubeconfig file which can be problematic from security reason
To make it clear, I own the cluster, I just want to give to some program restricted permissions

Answer 1

This is not straight forward. But still possible.
Create the namespace myns if not exists.
$ kubectl create ns myns
namespace/myns created
Create a service account cm-user in myns namespace. It'll create a secret token as well.
$ kubectl create sa cm-user -n myns
serviceaccount/cm-user created
$ kubectl get sa cm-user -n myns
NAME SECRETS AGE
cm-user 1 18s
$ kubectl get secrets -n myns
NAME TYPE DATA AGE
cm-user-token-kv5j5 kubernetes.io/service-account-token 3 63s
default-token-m7j9v kubernetes.io/service-account-token 3 96s
Get the token and ca.crt from cm-user-token-kv5j5 secret.
$ kubectl get secrets cm-user-token-kv5j5 -n myns -oyaml
Base64 decode the value of token from cm-user-token-kv5j5.
Now create a user using the decoded token.
$ kubectl config set-credentials cm-user --token=<decoded token value>
User "cm-user" set.
Now generate a kubeconfig file kubeconfig-cm.
apiVersion: v1
kind: Config
clusters:
- cluster:
certificate-authority-data: <ca.crt value from cm-user-token-kv5j5 secret>
server: <kubernetes server>
name: <cluster>
contexts:
- context:
cluster:<cluster>
namespace: myns
user: cm-user
name: cm-user
current-context: cm-user
users:
- name: cm-user
user:
token: <decoded token>
Now create a role and rolebinding for sa cm-user.
---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: myns
name: cm-user-role
rules:
- apiGroups: [""]
resources: ["configmaps"]
verbs: ["update", "get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
name: cm-user-rb
namespace: myns
roleRef:
apiGroup: rbac.authorization.k8s.io
kind: Role
name: cm-user-role
subjects:
- namespace: myns
kind: ServiceAccount
name: cm-user
We are done. Now using this kubeconfig file you can update the mycm configmap. It doesn't have any other privileges.
$ kubectl get cm -n myns --kubeconfig kubeconfig-cm
NAME DATA AGE
mycm 0 8s
$ kubectl delete cm mycm -n myns --kubeconfig kubeconfig-cm
Error from server (Forbidden): configmaps "mycm" is forbidden: User "system:serviceaccount:myns:cm-user" cannot delete resource "configmaps" in API group "" in the namespace "myns"

Answer 2

You need to use RBAC and define role and then bind that role to a user or serviceaccount using rolebinding
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
namespace: default
name: configmap-reader
rules:
- apiGroups: [""] # "" indicates the core API group
resources: ["configmaps"]
verbs: ["update", "get", "list"]
---
apiVersion: rbac.authorization.k8s.io/v1
# This role binding allows "jane" to read config maps in the "default" namespace.
# You need to already have a Role named "configmap-reader" in that namespace.
kind: RoleBinding
metadata:
name: read-configmap
namespace: default
subjects:
# You can specify more than one "subject"
- kind: User
name: jane # "name" is case sensitive
apiGroup: rbac.authorization.k8s.io
roleRef:
# "roleRef" specifies the binding to a Role / ClusterRole
kind: Role #this must be Role or ClusterRole
name: configmap-reader # this must match the name of the Role or ClusterRole you wish to bind to
apiGroup: rbac.authorization.k8s.io
https://kubernetes.io/docs/reference/access-authn-authz/rbac/