// ###################
// #  Login.aspx.cs  #
// ###################
protected void btnLogin_Click(object sender, EventArgs e)
{
    User us = new User(txtEmail.Text, txtPass.Text);
    if (us.Login() != null)
    {
        generateSessionVars(us);
        Response.Redirect("~/Members/Default.aspx");
    }
    else
    {
        lblErr.Text = "Invalid username or password.";
    }
}

// ######################
// #  App_Code/User.cs  #
// ######################
public class User
{
    public int userid { get; protected set; }
    public string email { get; protected set; }
    public string pass { get; protected set; }

    myDatabaseContext db = new myDatabaseContext(); // contains object user as returned by Login()

    public User(string EmailAddress, string Password)
    {
        email = EmailAddress;
        pass = Password;
    }

    public user Login()
    {
        string salt = getSalt();
        byte[] hash = HashPassword(pass, salt, SHA512);

        return user = (from u in db.users
                        where u.email == email and u.pass == hash
                        select u).FirstOrDefault();
    }

    private string getSalt()
    {
        var salt = (from u in db.users
                     where u.email == email
                     select u.salt).FirstOrDefault();

        if (salt != null)
        {
            return salt.salt;
        }
        else
        {
            return String.Empty;
        }
    }

    public byte[] HashPassword(string ClearPassword, string Salt, SHA512 algorithm)
    {
        byte[] data = new byte[];
        byte[] result;
        SHA512 shaM = new SHA512Managed();
        result = shaM.ComputeHash(data);
    }
}