To add an authorized user, that user should first create their own BSCpro account.
At the top right of the screen, click on your profile image OR you can click the down arrow next to your name and select "Profile".
Then, notice the tabs above the white box with your profile settings. Select "Authorized Users".
In the box below, simply search for the person by name that you would like to authorize to use your account. Then, don't forget to click "Update" and please note that you can only add up to 4 authorized users at one time.