V.AF - Viral and Frenzy gives you an excellent feature to safe guard your links from Unauthorized access.
There is a feature called as Password Protect your links, this way you are able to add a password to your link.
Then separately share the password to the people who should access the link to open the link.
This way you ensure that even though your link is shortened via a public URL Shortening service your link is safe with Viral & Frenzy.
We will soon add a Video giving you a tutorial how to "Password Protect" your links.
Team Viral and Frenzy