Is it better to use the asp.net security features or its better to write my own classes?

Hello,
I'm new here and I've been far from .net for few years, since asp.net 2 actually.
Now I'm in a project using asp.net 4 and got to study and update my skills.
Obviously a lot changed for good basically and something new to me is the set of features (controls and classes) to deal with security.
My questions are:
1) For a small application where I don't need a very fancy security module but a simple authentication feature and the ability of filtering data by user, still better to use the asp.net security features or its better to write my own classes?
2) Using asp.net security features, how is the best way of including new information regarding a user such as "department" and "project Id" from example?
 
Thanks in advance,
Vegas
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