As the title, Kubernetes already has a new component called `projected volume` that support the mounting of multiple secrets into one directory.

apiVersion: v1
kind: Pod
metadata:
  labels:
    run: my-app
  name: my-app
spec:
  containers:
  - command:
    - sleep
    - "3600"
    image: alpine
    name: alpine-secret
    volumeMounts:
    - name: my_secrets
      mountPath: "/var/secrets/"
      readOnly: true
  volumes:
  - name: my_secrets
    projected:
      sources:
      - secret:
          name: my-secret-one
      - secret:
          name: my-secret-two