The client secret value will remain valid forever as long as you don't regenerate it in the portal where you created the integration. If you're looking to see whether the client secret you're using is still valid, there isn't a way to see its validity but if it isn't valid anymore, you would get errors stating that something is invalid or there is malformed syntax (can't remember the exact error but would throw an error to this tune) in your request to the /v1/access_token API endpoint. It is not a full proof way to know that it's the client secret that's causing the issue as something else being wrong in the request could also throw those same errors but client secret would be one thing to check. In any case, if you're unsure whether client secret you're using is still valid, you're better off regenerating it in the portal.
As for the client ID, that is a unique value that will remain the same for as long as the integration is not deleted (in that case, client ID would not exist anymore of course).
