"policyRule": {
  "if": {
    "allOf": [
      {
        "field": "type",
        "equals": "Microsoft.Web/sites/config"
      },
      {
        "field": "name",
        "equals": "web"
      },
      {
        "field": "Microsoft.Web/sites/config/localMySqlEnabled",
        "exists": "true"
      },
      {
        "field": "Microsoft.Web/sites/config/localMySqlEnabled",
        "notEquals": "false"
      }
    ]
  },
  "then": {
    "effect": "Deny"
  }
}