Allow setting impersonation extras

[waterfoul]

Problem When an aks cluster is setup with EntraId Auth and Azure RBAC you need to pass "extra:oid" in order for impersonation to work. This means weave gitops' impersonation will not work. Example:

kubectl get GitRepository -A --as "user@domain.com"

Results in

Error from server (Forbidden): gitrepositories.source.toolkit.fluxcd.io is forbidden: User "user@domain.com" cannot list resource "gitrepositories" in API group "source.toolkit.fluxcd.io" at the cluster scope: Azure does not have opinion for this non AAD user. If you are an AAD user, please set Extra:oid parameter for impersonated user in the kubeconfig

If you create a user in your kubeconfig with

  user:
    as: user@domain.com
    as-user-extra:
      oid:
      - 00000000-0000-0000-0000-000000000000

along with the normal user config and use it the (via a new context) it works

Solution I'd like a feature to be able to map oidc claims to impersonation extras

Workaround I added oidcGroupsPrefix: "weave:" to my issuer secret then manually configured RBAC for specific groups using things like the following yaml. Not ideal since the whole point of using Azure RBAC is to centralize this sort of thing

apiVersion: rbac.authorization.k8s.io/v1
kind: ClusterRoleBinding
metadata:
  name: weave-global-admin
subjects:
- kind: Group
  name: weave:00000000-0000-0000-0000-000000000000
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: cluster-admin

Additional context

[bigkevmcd]

Simple implementation could accept a set of keys to lookup in the OIDC ID Token and store these on the UserPrincipal as a map.

It's a bit tricky because the values for the the Extra data are slices of strings, so, similar to the existing code, you'd need to parse these as strings or slices of strings, and convert the string to a slice when necessary.

Then inject these here https://github.com/weaveworks/weave-gitops/blob/2af6d1133a5717fc3b0f367734443557074b1548/pkg/kube/config_getter.go#L61 into the ImpersonationConfig.