You can password protect links in your account so only authorized people can view your links when you a new create a short link or you you want to protect an older shortened URL in your account. This is very easy to do. Just login and go to the “New Shorten Link” button:

and in that new window add your link that you want to be shortened and protected and click on the “Advanced Option” button: 

and the enter the password and click save, (The “Shorten” button) as seen in below recording.

After that your links will be protected.

However it is important to understand that you can only use the security Page Redirect and not the “Direct Redirect” because using the setting of “Direct Redirect” will override the password protection and send any visitor to the final destination without the need to enter a password: