how to authenticate using persons windows login ?

You should go there-[Authenticating Users with Windows Authentication][^] to learn how to authenticate user with windows authentication.

Perhaps you want to make your application to run on local intranet for limited users(with their windows credentials). For this you can go for windows authentication:

Windows Authentication Using Form Authentication[^]

hope it helps :)

use window authentication
+
checks

Dim WinId As String = HttpContext.Current.User.Identity.Name
       user.Text = WinId.ToString
       Pass.Text = HttpContext.Current.User.Identity.IsAuthenticated.ToString
       Pass0.Text = HttpContext.Current.User.Identity.AuthenticationType

Check this code help you to which user is login and its is window authenticated or not.

i have used the VS login in tool in my webpage
then add the below into the webconfig

<connectionstrings>
    <remove name="LocalSqlServer"></remove>
    <add name="accconstr" connectionstring="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|DB.mdb" providername="System.Data.OleDb"></add>
    <add name="ADConnectionString" connectionstring="LDAP:SERVERNAME"></add>
  </connectionstrings>
  <system.web>
    <identity impersonate="true" username="AD ADMIN USERNAME" password="AD ADMIN PASSWORD"></identity>
    <membership defaultprovider="MembershipADProvider">
      <providers>
        <remove name="AspNetSqlMembershipProvider"></remove>
        <add connectionstringname="ADConnectionString" attributemapusername="sAMAccountName" name="MembershipADProvider" type="System.Web.Security.ActiveDirectoryMembershipProvider, System.Web, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a"></add>
      </providers>
    </membership>

</system.web>
<authentication mode="Forms">
      <forms loginUrl="login.aspx" protection="All" timeout="30" name="AppNameCookie" slidingExpiration="true" cookieless="UseCookies" enableCrossAppRedirects="false"/>
    </authentication>
    <authorization>
      <deny users="?" />
      <allow users="*" />
    </authorization>

if you have an active directory, you can use use that to authenticate the users before they enter into you website.
let me know if you have Active Directory and the credentials to use that. maybe i can help you with the code as i had recently used it myself for a corporate intranet.