Authentication help.

Hi all

I am new to asp.net. I want to implement authentication in all pages.
What i want to do is validate user from database table. So currently
what i am doing is on login page validating user and storing valid
user id in sesstion.

On every page i am checking userid from session.. But i don't want to
behavirour. what i want is to provide authentication to all pages
once not on every page .

So how will i do this. And if session expire in between what will
happen if user try to access the page after that.

Please correct me if i am wrong in any concept.

thanks in advance.

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