Validate User Id and Password with AD

string username ="ABC";
string password="abc";
bool result =false;
string domain = System.Configuration.ConfigurationSettings.AppSettings["Domain"];
using (PrincipalContext pc = new PrincipalContext(ContextType.Domain, domain))
{
result =pc.ValidateCredentials(username, password);
}
if( result )
{
alert("User validated");
}