<connectionStrings>
  <add name="ADConn" connectionString="LDAP://YourConnection" />
</connectionStrings>

<membership defaultProvider="ADMembership">
  <providers>
    <add name="ADMembership"
         type="System.Web.Security.ActiveDirectoryMembershipProvider,
               System.Web,
               Version=2.0.0.0,
               Culture=neutral,
               PublicToken=b03f5f7f11d50a3a"
         connectionStringName="ADConn"
         connectionUsername="domain/user"
         connectionPassword="pwd" />
  </providers>
</membership>

<system.web>
  <authentication mode="Windows" />

  <authorization>
    <deny users="?" />
  </authorization>
</system.web>

@User.Identity.Name