Magento itself have functionality of token expiration time. Where you can set expiration time for token.(Store->Configuration->OAuth->Access Token Expiration)
Once token gets expired - generate token again and get the new token.
So every time when token gets expired generate new token by either cron or manually and store it in either default magento token box or you can store in your custom textbox as well and get the value of token from there.
To make ease you can also get the new token value by cron on specific time or on when token change condition applied.
So even though hacker gets the token once , it will still not works after specific time.
According to me its best approach to provide more security for token management.
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