Allow only specific values for key in Joi schema

You can also use valid like

const schema = joi.object().keys({
  query: joi.object().keys({
    // allow only apple and banana
    id: joi.string().valid('apple','banana').required(),
  }).required(),
})

Reference: https://github.com/hapijs/joi/blob/v13.1.2/API.md#anyvalidvalue—aliases-only-equal