How Do I Authenticate The Page In Asp.Net C#

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C#

Below is the methods I was written in DAL layer

public DataSet IsLoginCheck()
      {

          try
          {
              string connectionString = sql.ConnectionString();
              SqlConnection con = new SqlConnection();
              con.ConnectionString = connectionString;
              con.Open();
              SqlCommand cmd = new SqlCommand("GetUser", con);
              cmd.CommandType = CommandType.StoredProcedure;
              cmd.Parameters.AddWithValue("@UserID", objBOL._UserName);
              SqlDataAdapter da = new SqlDataAdapter();
              DataSet ds = new DataSet();
              da = new SqlDataAdapter(cmd);
              da.Fill(ds);
              con.Close();
              return ds;
          }
              catch
               {
                  throw;
              }

          }

======================================================================
Below are the methods I was written in BLL layer

public bool IsAuthenticated(string username, string pwd)
      {
           _path="LDAP://#";
           string domainAndUsername = "#" + @"\" + username;
          DirectoryEntry entry = new DirectoryEntry(_path, domainAndUsername, pwd);

          try
          {
              //Bind to the native AdsObject to force authentication.
              object obj = entry.NativeObject;

              DirectorySearcher search = new DirectorySearcher(entry);

              search.Filter = "(SAMAccountName=" + username + ")";
              search.PropertiesToLoad.Add("cn");
              SearchResult result = search.FindOne();

              if (null == result)
              {
                  return false;
              }

              //Update the new path to the user in the directory.
              _path = result.Path;
              _filterAttribute = (string)result.Properties["cn"][0];
          }
          catch 
          {
              throw;   
          }

          return true;
      }

------------------------------

public DataSet Login()
     {
         DataSet ds = new DataSet();
         ds = _LoginDAL.IsLoginCheck();// Calling of Data layer function
         return ds;
     }

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Please help me how do I authenticate the ad username in UI.

-If AD useraname and pwd correct means send to next page else it shows error

Help me please.