Allow per user based kubelogin lock file

[tommylogik]

Purpose of this feature

---

In a multi-user environment we need to be able to simultaneously have users login to a kubernetes cluster.

Updating this method to go from using the os temp directory to using the user home directory to create the generated lock filename allows for multi-user capable login. If the user doesn't have the proper environment variable set (HOME,USERPROFILE,home), it falls back to the default temp directory.

Current workaround

---

The current workaround for this functionality is to temporarily set TMPDIR env variable to the users home directory and then reset it to the temp directory

For example:

$ export OLD_TMPDIR=$(echo $TMPDIR)
$ kubectl oidc-login
$ export TMPDIR=$(echo $OLD_TMPDIR)

This will work for the time being but I would love to not have to implement this workaround and have it part of the core functionality of kubelogin's master branch.

[MioOgbeni]

I would also appreciate this PR. Can you review it @int128?

[reinka]

Same here :) Ping @int128

[R-Studio]

Same issue here. 😒

Workaround

• Add the TMPDIR variable in kubeconfig in the users section. (Please replace <USERNAME> with your username!):

...
users:
- name: oidc
  user:
    exec:
      apiVersion: client.authentication.k8s.io/v1beta1
      args:
      - oidc-login
      - get-token
      - --oidc-issuer-url=https://<YOUR_KEYCLOAK>/realms/<REALM_NAME>
      - --oidc-client-id=kubernetes
      - --oidc-client-secret=<REDACTED>
      - --oidc-extra-scope=email
      - --oidc-extra-scope=groups
      command: kubectl
      env:
      - name: TMPDIR
        value: /home/<USERNAME>
      interactiveMode: IfAvailable
      provideClusterInfo: false

[int128]

This issue has been resolved by #1126