Joi does allow conditional validations. https://github.com/hapijs/joi/blob/v9.0.4/API.md#anywhenref-options .

What kind of validation are you doing on multiple values? Joi has things like https://github.com/hapijs/joi/blob/v9.0.4/API.md#objectxorpeers where multiple keys are used.

What are you doing that necessitates async validation? Making an API call?