KUBE_TOKEN=$(</var/run/secrets/kubernetes.io/serviceaccount/token)
NAMESPACE=myapp-dev
CONFIGMAP_NAME=testconfig
curl -sSk \
  -X PATCH \
  -d @- \
  -H "Authorization: Bearer $KUBE_TOKEN" \
  -H 'Accept: application/json' \
  -H'Content-Type: application/strategic-merge-patch+json' \
  https://$KUBERNETES_SERVICE_HOST:$KUBERNETES_PORT_443_TCP_PORT/api/v1/namespaces/$NAMESPACE/configmaps/$CONFIGMAP_NAME <<'EOF'
{
  "kind": "ConfigMap",
  "apiVersion": "v1",
  "data": {
    "foo": "bar"
  }
}
EOF