Adding a 2nd Email Field to Register Form to Confirm Address is Correct

I would like to know how I can add a second email field to the registration form so that when a user signs up, they enter the email in once for the system, and once more to make sure they didn't typo their email address.

This secondary email field doesn't need to be saved, it only needs to check against the first email field and if it's different, break the operation and require it be corrected.

We have confirmation emails turned off.