Authentication checking

[eluser]someone [/eluser]
Hello,

I'm going to write some little authentication for my news system, but I don't know how to check authentication from some other controller.

So I will write controller with name Authentication and I would like to check auth in other controller which is named Admin. To this controller can access only those who are logged in (for now, after I will create user groups) and nobody else. I have never used construct in my controller so I don't know what do I have to type in it to restrict access to non-users.

Thanks for help! :-)