helm-external-secrets/docs/snippets/vault-mtls-store.yaml

apiVersion: external-secrets.io/v1beta1
kind: SecretStore
metadata:
  name: vault-backend
  namespace: example
spec:
  provider:
    vault:
      server: "https://vault.acme.org"
      path: "secret"
      version: "v2"

      # client TLS related configuration
      caBundle: "..."
      tls:
        clientCert:
          name: "my-cert-secret"
          key: "tls.crt"
        secretRef:
          name: "my-cert-secret"
          key: "tls.key"

      # the authentication methods are not really related to the client TLS configuration
      auth:
        ...