in the users table you would need to have a verified column that is set to 0 by default.
on the new user page, they would need to input the user name they registered with and the rest of the info.
then use an update record behavior from data assist to update the user record, update the verified column to 1 and add the rest of the info, use the username as a lookup.
also, updaate the authenticate user behavior on the login page, add a condition on the second page, select the verified column and set the value = to 1.