Try Vault with MySQL storage backend (via Docker)

docker-compose.yml

version: '2'
services:
  mcba-vault:
    container_name: mcba-vault
    image: vault:latest
    restart: unless-stopped
    volumes:
      - ./vault.hcl:/etc/vault.hcl
    links:
      - "mcba-mysql:mcba-mysql"
    ports:
      - 8200:8200
    command: "server -config=/etc/vault.hcl"

  mcba-mysql:
    container_name: mcba-mysql
    image: mysql:5.7
    ports:
      - 3306:3306
    environment:
      MYSQL_ALLOW_EMPTY_PASSWORD: "true"
      MYSQL_ROOT_PASS: secret
      MYSQL_USER: foo
      MYSQL_PASSWORD: bar
      MYSQL_DATABASE: vault

INIT_VAULT.md

Initialise (will return keys and a token)

curl -X PUT http://0.0.0.0:8200/v1/sys/init --data '{"secret_shares":1, "secret_threshold":1}'

Use one of the keys to unseal

curl -X PUT http://0.0.0.0:8200/v1/sys/unseal --data '{"key":"a5e665962f544dd16471c120c5500a7906cfbaeb3f18ae0fc6c5c71d444f0a90"}'

Use the root token to store something

curl -X PUT http://0.0.0.0:8200/v1/secret/foo/bar -H "X-Vault-Token: f9bd7f8c-4234-e3de-acad-076682dd2733" --data '{"some_api_key":"bzzp"}'

vault.hcl

backend "mysql" {
 address = "mcba-mysql:3306"
 username = "foo"
 password = "bar"
}

listener "tcp" {
 address = "0.0.0.0:8200"
 tls_disable = 1
}

disable_mlock = true