FormsAuthentication doesn't work from separate code file.

I'm trying to hash passwords for a login system with the FormsAuthentication.HashPasswordForStoringInConfigFile() function. I have a test button click function for this purpose:


protected void button_Click(object sender, EventArgs e)
    {
        label.Text = FormsAuthentication.HashPasswordForStoringInConfigFile(password.Text, "SHA1");
    }


It works fine when I put this within the <script> tags on the same page but when I cut and paste the same function in a separate code file, it doesn't work. It says FormsAuthentication does not exist in this context.
Please help?


P.S: I am not salting the passwords and don't need to right now. Thanks.

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