how to get username password from window active directory

// set up domain context
PrincipalContext ctx = new PrincipalContext(ContextType.Domain);

// find user by name
UserPrincipal user = UserPrincipal.FindByIdentity(ctx, "John Doe");

// if we found user - inspect its details
if(user != null)
{
    string firstName = user.GivenName;
    string lastName = user.Surname;
    string email = user.EmailAddress;
    string phone = user.VoiceTelephoneNumber;
}