Asp.net Page Login Validation

Use Forms Authentication.
Use some thing like this at web.config

<location path="secure">
    <system.web>
      <authorization>
        <deny users="?"/>
        <deny users="jhon"/>
      </authorization>
    </system.web>
  </location>

secure is a folder which contains your secure webforms.

<authentication mode="Forms">
      <forms loginUrl="Default.aspx"
           protection="All"
           timeout="30"
           name=".ASPXAUTH"
           path="/"
           requireSSL="false"
           slidingExpiration="true"
           defaultUrl="default.aspx"
           cookieless="UseDeviceProfile"
           enableCrossAppRedirects="false" >
        <credentials passwordFormat="Clear">
          <user name="kim" password="kim@123"/>
          <user name="jhon" password="jhonn"/>
        </credentials>
      </forms>
    </authentication>

Now at server side code

Default.aspx is your login form, Drag Two TextBoxes and a Button
at click event of button write following code. Default2.aspx is destination page. Secure is a folder which can have webforms which you wants to make secure

if (FormsAuthentication.Authenticate(TextBox1.Text, TextBox2.Text))
        {
            FormsAuthentication.SetAuthCookie(
                 this.TextBox1.Text.Trim(), false);

            FormsAuthenticationTicket ticket1 =
               new FormsAuthenticationTicket(
                    1,                                   // version
                    this.TextBox1.Text.Trim(),   // get username  from the form
                    DateTime.Now,                        // issue time is now
                    DateTime.Now.AddMinutes(10),         // expires in 10 minutes
                    false,      // cookie is not persistent
                    "HR"                              // role assignment is stored
                // in userData
                    );
            HttpCookie cookie1 = new HttpCookie(
              FormsAuthentication.FormsCookieName,
              FormsAuthentication.Encrypt(ticket1));
            Response.Cookies.Add(cookie1);

            // 4. Do the redirect. 
            String returnUrl1;
            // the login is successful
            if (Request.QueryString["ReturnUrl"] == null)
            {
                returnUrl1 = "Default2.aspx";
            }

            //login not unsuccessful 
            else
            {
                returnUrl1 = Request.QueryString["ReturnUrl"];
            }
            Response.Redirect(returnUrl1);

        }