How to set the second value when a required field is validated?

[Du-Nguyen]

Runtime

Node js

Runtime version

Node 18

Module version

"joi": "^17.13.3",

Used with

No response

Any other relevant information

No response

How can we help?

When validating, if the value does not exist, set the second value from an environment variable; if it is still unavailable, make it required.
I tried implementing it as below, and it seems to work. Is it okay?

 var: Joi.string()
        .required()
        .failover(() => process.env.VAR),