dashboard: Dashboard --token-ttl is not working

Environment

Dashboard version: 1.8.3 Kubernetes version: 1.9.3 Operating system: Ubuntu LTS 16.04

Steps to reproduce

1. Setup tokens in the api-server using --token-auth-file=/etc/kubernetes/pki/tokens.csv and restart
2. Add --token-ttl=43200 to the dashboard deployment and restart

Observed result

1. Log on to the dashboard using a token
2. Wait for 20 minutes
3. Attempt to use dashboard
4. Requires logging on again as it appear jwe still expiring after 15 minutes

Expected result

That the jwetoken remains valid for 12 hours and we will not require authenticating until the 12 hours are up.

Comments

dashboard deployment yaml:-

kind: Deployment
apiVersion: apps/v1beta2
metadata:
  labels:
    k8s-app: kubernetes-dashboard
  name: kubernetes-dashboard
  namespace: kube-system
spec:
  replicas: 1
  revisionHistoryLimit: 10
  selector:
    matchLabels:
      k8s-app: kubernetes-dashboard
  template:
    metadata:
      labels:
	k8s-app: kubernetes-dashboard
    spec:
      containers:
      - name: kubernetes-dashboard
        image: k8s.gcr.io/kubernetes-dashboard-amd64:v1.8.3
        ports:
	- containerPort: 8443
          protocol: TCP
        args:
          - --tls-key-file=k8sm.key
          - --tls-cert-file=k8sm.crt
          - --token-ttl=43200
        volumeMounts:
        - name: kubernetes-dashboard-certs
          mountPath: /certs
        - mountPath: /tmp
          name: tmp-volume
        livenessProbe:
          httpGet:
            scheme: HTTPS
            path: /
            port: 8443
          initialDelaySeconds: 30
          timeoutSeconds: 30
      volumes:
      - name: kubernetes-dashboard-certs
        secret:
          secretName: kubernetes-dashboard-certs
      - name: tmp-volume
        emptyDir: {}
      serviceAccountName: kubernetes-dashboard
      tolerations:
      - key: node-role.kubernetes.io/master
        effect: NoSchedule
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
              - matchExpressions:
                - key: "node-role.kubernetes.io/master"
                  operator: "Exists"