Access Control

kty utilizes external systems for both authn and authz. To fetch your identity, a combo of OpenID and the keys resource in your cluster are used. These map from something external (an oauth identity token or a public key hash) to a User and Group inside of k8s.

Similar to authentication, kty does not do authorization itself. Instead, it impersonates the authenticated user. Any action that is taken from that point forward uses the users’ permissions as granted via. RBAC in k8s.

Flow

Authentication

There are two ways for an incoming SSH session to get a user identity:

OpenID - If the user does not have an authorized public key, the SSH session prompts with an open id flow. When that flow is successful, the returned token is mapped to a k8s identity. By default, this is the email claim in the identity token. If you would like to map different claims and/or add groups, take a look at the server configuration.
Public Key - By default, once a user has been authenticated with openid, they will have a public key. This will contain the user and group information extracted from the identity token. If you would like to skip OpenID entirely, you can create Key resources, the kty users key can be used to do this as an alternative to kubectl.

To validate that a user has access, you can use the kty users check command. This is a great way to debug why users are not being allowed to connect.

kty users check [email protected]

Authorization

To be authorized, either the name or groups for a user need to have role bindings added to the cluster. The kty users grant command is one way to go about this, but it is purposely naive. To do something more flexible, you can check out kubectl:

kubectl create clusterrolebinding foo-bar-com --clusterrole=<my-role> [email protected]

Note that you can use a RoleBinding instead, but only for specific functionality.

SSH

The minimum permissions are:

resources: ['pods']
verbs: ['list', 'watch']

To see logs:

resources: ['"pods/log']
verbs: ['get']

To get a shell:

resources: ['pods/exec']
verbs: ['create']

Note: without the full permissions it is possible that the dashboard has some issues rendering.

Ingress Tunnel (`ssh -L`)

For each supported resource type (nodes, services, pods), you need:

create for resource/proxy
get for resource

Notes:

resourceNames works for these but it is a little unwieldy for names that are auto-generated such as node and pod.
For namespaced resources (services, pods), this can be a RoleBinding.

Here’s an example role for pods:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: my-role
rules:
  - apiGroups: ['']
    resources:
      - pods/proxy
    verbs:
      - create
    # resourceNames:
    #   - my-statefulset-0
  - apiGroups: ['']
    resources:
      - pods
    verbs:
      - get

Egress Tunnel (`ssh -L`)

The minimum permissions are:

resources: ['services', 'endpointslices']
verbs: ['patch']

SFTP(SCP)

To support scp, the minimum permissions are:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: my-role
rules:
  - apiGroups: ['']
    resources:
      - pods/exec
    verbs:
      - create
  - apiGroups: ['']
    resources:
      - pods
    verbs:
      - get

This will allow fetching files directly in addition to listing files that are pod specific (eg /<namespace>/<pod>/<container>).

To list files at the cluster level, you’ll need to add:

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRole
metadata:
  name: my-role
rules:
  - apiGroups: ['']
    resources:
      - pods
      - namespaces
    verbs:
      - get
      - list

Architecture Installation