Approvals - how to require login?

My university has a Smartsheet site license. I can clearly see everyone in the contact list. I am creating a very sensitive workflow that requires department head approvals and have setup a smooth automated workflow to accomplish this.

However, I just learned that ANYONE with the link can make an approval and the LastModifiedBy field simply captures the intended account, but not necessarily the person who actually pressed Approve, since they did not have to login.

There must be a simple way to require that Approvers login to Smartsheet prior to approving. What am I missing?

Thanks in advance!


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