I'm testing an installation of velero for k8s backups on AKS (Azure's kubernetes paas) and getting this error after a timeout period:

time="2019-10-14T11:22:56Z" level=info msg="Checking existence of namespace" logSource="pkg/cmd/server/server.go:336" namespace=velero
time="2019-10-14T11:22:56Z" level=info msg="Namespace exists" logSource="pkg/cmd/server/server.go:342" namespace=velero
time="2019-10-14T11:22:59Z" level=info msg="Checking existence of Velero custom resource definitions" logSource="pkg/cmd/server/server.go:371"
time="2019-10-14T11:22:59Z" level=info msg="All Velero custom resource definitions exist" logSource="pkg/cmd/server/server.go:405"
time="2019-10-14T11:22:59Z" level=info msg="Checking that all backup storage locations are valid" logSource="pkg/cmd/server/server.go:412"
An error occurred: some backup storage locations are invalid: error getting backup store for location "default": rpc error: code = Unknown desc = azure.BearerAuthorizer#WithAuthorization: Failed to refr
esh the Token for request to https://management.azure.com/subscriptions/<subscription_id>/resourceGroups/rsg-lolgroup/providers/Microsoft.Storage/storageAccounts/lolsubs/listKeys?api-version=2018-02-01: StatusCode=0 -- Original Error: adal: Failed to execute the refresh request. Error = 'Post https://login.microsoftonline.com/tenant_id/oauth2/token?api-version=1.0: x509: certificate signed by unknown authority'

• Turning velero debug higher (-v10) doesn't shed further light, we see the REST responses from the api without any obvious error:

{
  "kind": "Deployment",
  "apiVersion": "apps/v1",
  "metadata": {
    "name": "velero",
    "namespace": "velero",
    "selfLink": "/apis/apps/v1/namespaces/velero/deployments/velero",
    "uid": "redacted",
    "resourceVersion": "701159",
    "generation": 1,
    "creationTimestamp": "2019-10-14T06:18:45Z",
    "labels": {
      "component": "velero"
    },
    "annotations": {
      "deployment.kubernetes.io/revision": "1"
    }
  },
  "spec": {
    "replicas": 1,
    "selector": {
      "matchLabels": {
        "deploy": "velero"
      }
    },
    "template": {
      "metadata": {
        "creationTimestamp": null,
        "labels": {
          "component": "velero",
          "deploy": "velero"
        },
        "annotations": {
          "prometheus.io/path": "/metrics",
          "prometheus.io/port": "8085",
          "prometheus.io/scrape": "true"
        }
      },
      "spec": {
        "volumes": [
          {
            "name": "plugins",
            "emptyDir": {}
          },
          {
            "name": "scratch",
            "emptyDir": {}
          },
          {
            "name": "cloud-credentials",
            "secret": {
              "secretName": "cloud-credentials",
              "defaultMode": 420
            }
          }
        ],
        "containers": [
          {
            "name": "velero",
            "image": "docker-rtsre-local.lol.com:8443/velero:0.0.1",
            "command": [
              "/velero"
            ],
            "args": [
              "server"
            ],
            "ports": [
              {
                "name": "metrics",
                "containerPort": 8085,
                "protocol": "TCP"
              }
            ],
            "env": [
              {
                "name": "VELERO_SCRATCH_DIR",
                "value": "/scratch"
              },
              {
                "name": "VELERO_NAMESPACE",
                "valueFrom": {
                  "fieldRef": {
                    "apiVersion": "v1",
                    "fieldPath": "metadata.namespace"
                  }
                }
              },
              {
                "name": "GOOGLE_APPLICATION_CREDENTIALS",
                "value": "/credentials/cloud"
              },
              {
                "name": "AWS_SHARED_CREDENTIALS_FILE",
                "value": "/credentials/cloud"
              },
              {
                "name": "AZURE_CREDENTIALS_FILE",
                "value": "/credentials/cloud"
              }
            ],
            "resources": {
              "limits": {
                "cpu": "1",
                "memory": "256Mi"
              },
              "requests": {
                "cpu": "500m",
                "memory": "128Mi"
              }
            },
            "volumeMounts": [
              {
                "name": "plugins",
                "mountPath": "/plugins"
              },
              {
                "name": "scratch",
                "mountPath": "/scratch"
              },
              {
                "name": "cloud-credentials",
                "mountPath": "/credentials"
              }
            ],
            "terminationMessagePath": "/dev/termination-log",
            "terminationMessagePolicy": "File",
            "imagePullPolicy": "Always"
          }
        ],
        "restartPolicy": "Always",
        "terminationGracePeriodSeconds": 30,
        "dnsPolicy": "ClusterFirst",
        "serviceAccountName": "velero",
        "serviceAccount": "velero",
        "securityContext": {},
        "schedulerName": "default-scheduler"
      }
    },
    "strategy": {
      "type": "RollingUpdate",
      "rollingUpdate": {
        "maxUnavailable": "25%",
        "maxSurge": "25%"
      }
    },
    "revisionHistoryLimit": 10,
    "progressDeadlineSeconds": 600
  },
  "status": {
    "observedGeneration": 1,
    "replicas": 1,
    "updatedReplicas": 1,
    "unavailableReplicas": 1,
    "conditions": [
      {
        "type": "Progressing",
        "status": "True",
        "lastUpdateTime": "2019-10-14T06:21:35Z",
        "lastTransitionTime": "2019-10-14T06:18:45Z",
        "reason": "NewReplicaSetAvailable",
        "message": "ReplicaSet \"velero-866985f74d\" has successfully progressed."
      },
      {
        "type": "Available",
        "status": "False",
        "lastUpdateTime": "2019-10-14T07:03:46Z",
        "lastTransitionTime": "2019-10-14T07:03:46Z",
        "reason": "MinimumReplicasUnavailable",
        "message": "Deployment does not have minimum availability."
      }
    ]
  }
  }
}

I suspect this could be firewall be related, but is there a way to debug further?