helm-external-secrets/config/certmanager/certificate.yaml

# The following manifests contain a self-signed issuer CR and a certificate CR.
# More document can be found at https://docs.cert-manager.io
# WARNING: Targets CertManager 0.11 check https://docs.cert-manager.io/en/latest/tasks/upgrading/index.html for 
# breaking changes
apiVersion: cert-manager.io/v1alpha2
kind: Issuer
metadata:
  name: selfsigned-issuer
  namespace: system
spec:
  selfSigned: {}
---
apiVersion: cert-manager.io/v1alpha2
kind: Certificate
metadata:
  name: serving-cert  # this name should match the one appeared in kustomizeconfig.yaml
  namespace: system
spec:
  # $(SERVICE_NAME) and $(SERVICE_NAMESPACE) will be substituted by kustomize
  dnsNames:
  - $(SERVICE_NAME).$(SERVICE_NAMESPACE).svc
  - $(SERVICE_NAME).$(SERVICE_NAMESPACE).svc.cluster.local
  issuerRef:
    kind: Issuer
    name: selfsigned-issuer
  secretName: webhook-server-cert # this secret will not be prefixed, since it's not managed by kustomize